Polynuclear platinum phosphanido/phosphinito complexes: formation of P-O and P-O-P bonds through reductive coupling processes.

A mixture of the asymmetric complexes of formula [(RF)2Pt(µ-Ph2PO)(µ-PPh2)Pt(µ-PPh2)2Pt(solv)(solv')] [(1-(solv)(solv')] (solv, solv' = acetone, H2O, CH3CN) has been prepared by reaction of [(RF)2Pt(II)(µ-PPh2)2Pt(II)(µ-PPh2)2Pt(II)(NCCH3)2] with AgClO4 in CH3CN/acetone. The lability of the Pt-solvent bonds allows the displacement of the coordinated solvent molecules by dppm or Cl(-) and the isolation of the tri- or hexanuclear phosphanido/phosphinito Pt(ii) complexes [(C6F5)2Pt(µ-PPh2)(µ-PPh2O)Pt(µ-PPh2)2Pt(dppm)] (2) or [NBu4]2[(C6F5)2Pt(µ-PPh2)(µ-PPh2O)Pt(µ-PPh2)2Pt(µ-Cl)2Pt(µ-PPh2)2Pt(µ-PPh2)(µ-PPh2O)Pt(C6F5)2] (as a mixture of the two possible isomers 4a and 4b). Complex 2 reacts with AgClO4 to form the tetranuclear derivative [(C6F5)2Pt(µ-PPh2)(µ-PPh2O)Pt(µ-PPh2)2Pt(dppm)Ag(OClO3)] (3), which displays two Pt-Ag donor-acceptor bonds. The mixture of the hexanuclear isomers 4a-4b reacts with Tl(acac) producing the acetylacetonato complex [NBu4][(C6F5)2Pt(µ-PPh2)(µ-PPh2O)Pt(µ-PPh2)2Pt(acac)] (5) which, upon reaction with HCl, yields back the mixture of 4a-4b. The reaction of 4a-4b with PPh3 produces [NBu4][(C6F5)2Pt(µ-PPh2)(µ-PPh2O)Pt(µ-PPh2)2Pt(Cl)(PPh3)] (6) as a mixture of isomers with the chloro ligand located syn (6a) or anti (6b) to the PPh2O(-) group. Either the reaction of 6 with AgClO4 or the treatment of 5 with HPPh3ClO4 results in the formation of the species [(C6F5)2Pt(II)(µ-PPh2)2Pt(I)(µ-PPh2OPPh2)Pt(I)(PPh3)] (7) (44 VEC), which can be explained as the consequence of a PPh2O/PPh2 reductive coupling and a rearrangement of ligands in the molecule generating a Pt(ii),Pt(i),Pt(i) compound. All complexes were characterised in the solid state by XRD (only one of the isomers, in the cases of 4 and 6) and in solution by NMR spectroscopy.

An Extended Chain and Trinuclear Complexes Based on Pt(II)-M (M = Tl(I), Pb(II)) Bonds: Contrasting Photophysical Behavior.

The syntheses and structural characterizations of a Pt-Tl chain [{Pt(bzq)(C6F5)2}Tl(Me2CO)]n 1 and two trinuclear Pt2M clusters (NBu4)[{Pt(bzq)(C6F5)2}2Tl] 2 and [{Pt(bzq)(C6F5)2}2Pb] 3 (bzq = 7,8-benzoquinolinyl), stabilized by donor-acceptor Pt → M bonds, are reported. The one-dimensional heterometallic chain 1 is formed by alternate "Pt(bzq)(C6F5)2" and "Tl(Me2CO)" fragments, with Pt-Tl bond separations in the range of 2.961(1)-3.067(1) Å. The isoelectronic trinuclear complexes 2 (which crystallizes in three forms, namely, 2a, 2b, and 2c) and 3 present a sandwich structure in which the Tl(I) or Pb(II) is located between two "Pt(bzq)(C6F5)2" subunits. NMR studies suggest equilibria in solution implying cleavage and reformation of Pt-M bonds. The lowest-lying absorption band in the UV-vis spectra in CH2Cl2 and tetrahydrofuran (THF) of 1, associated with (1)MLCT/(1)L'LCT (1)[5dπ(Pt) → π*(bzq)]/(1)[(C6F5) → bzq], displays a blue shift in relation to the precursor, suggesting the cleavage of the chain maintaining bimetallic Pt-Tl fragments in solution, also supported by NMR spectroscopy. In 2 and 3, it shows a blue shift in THF and a red shift in CH2Cl2, supporting a more extensive cleavage of the Pt-M bonds in THF solutions than in CH2Cl2, where the trinuclear entities are predominant. The Pt-Tl chain 1 displays in solid state a bright orange-red emission ascribed to (3)MM'CT (M' = Tl). It exhibits remarkable and fast reversible vapochromic and vapoluminescent response to donor vapors (THF and Et2O), related to the coordination/decoordination of the guest molecule to the Tl(I) ion, and mechanochromic behavior, associated with the shortening of the intermetallic Pt-Tl separations in the chain induced by grinding. In frozen solutions (THF, acetone, and CH2Cl2) 1 shows interesting luminescence thermochromism with emissions strongly dependent on the solvent, concentration, and excitation wavelengths. The Pt2Tl complex 2 shows an emission close to 1, ascribed to charge transfer from the platinum fragment to the thallium [(3)(L+L')MM'CT]. 2 also shows vapoluminescent behavior in the presence of vapors of Me2CO, THF, and Et2O, although smaller and slower than those of 1. The trinuclear neutral complex Pt2Pb 3 displays a blue-shift emission band, tentatively assigned to admixture of (3)MM'CT (3)[Pt(d) → Pb(sp)] with some metal-mediated intraligand ((3)ππ/(3)ILCT) contribution. In contrast to 1 and 2, 3 does not show vapoluminescent behavior.

Addition of nucleophiles to phosphanido derivatives of Pt(III): formation of P-C, P-N, and P-O bonds.

The reactivity of the dinuclear platinum(III) derivative [(R(F))2Pt(III)(µ-PPh2)2Pt(III)(R(F))2](Pt-Pt) (R(F) = C6F5) (1) toward OH(-), N3(-), and NCO(-) was studied. The coordination of these nucleophiles to a metal center evolves with reductive coupling or reductive elimination between a bridging diphenylphosphanido group and OH(-), N3(-), and NCO(-) or C6F5 groups and formation of P-O, P-N, or P-C bonds. The addition of OH(-) to 1 evolves with a reductive coupling with the incoming ligand, formation of a P-O bond, and the synthesis of [NBu4]2[(R(F))2Pt(II)(µ-OPPh2)(µ-PPh2)Pt(II)(R(F))2] (3). The addition of N3(-) takes place through two ways: (a) formation of the P-N bond and reductive elimination of PPh2N3 yielding [NBu4]2[(R(F))2Pt(II)(µ-N3)(µ-PPh2)Pt(II)(R(F))2] (4a) and (b) formation of the P-C bond and reductive coupling with one of the C6F5 groups yielding [NBu4][(R(F))2Pt(II)(µ-N3)(µ-PPh2)Pt(II)(R(F))(PPh2R(F))] (4b). Analogous behavior was shown in the addition of NCO(-) to 1 which afforded [NBu4]2[(R(F))2Pt(II)(µ-NCO)(µ-PPh2)Pt(II)(R(F))2] (5a) and [NBu4][(R(F))2Pt(II)(µ-NCO)(µ-PPh2)Pt(II)(R(F))(PPh2R(F))] (5b). In the reaction of the trinuclear complex [(R(F))2Pt(III)(µ-PPh2)2Pt(III)(µ-PPh2)2Pt(II)(R(F))2](Pt(III)-Pt(III)) (2) with OH(-) or N3(-), the coordination of the nucleophile takes place selectively at the central platinum(III) center, and the PPh2/OH(-) or PPh2/N3(-) reductive coupling yields the trinuclear [NBu4]2[(R(F))2Pt(II)(µ-Ph2PO)(µ-PPh2)Pt(II)(µ-PPh2)2Pt(II)(R(F))2] (6) and [NBu4][(R(F))2Pt(1)(µ3-Ph2PNPPh2)(µ-PPh2)Pt(2)(µ-PPh2)Pt(3)(R(F))2](Pt(2)-Pt(3)) (7). Complex 7 is fluxional in solution, and an equilibrium consisting of Pt-Pt bond migration was ascertained by (31)P EXSY experiments.

Oxidatively induced P-O bond formation through reductive coupling between phosphido and acetylacetonate, 8-hydroxyquinolinate, and picolinate groups.

The dinuclear anionic complexes [NBu4][(RF)2M(II)(µ-PPh2)2M'(II)(N(^)O)] (RF = C6F5. N(^)O = 8-hydroxyquinolinate, hq; M = M' = Pt 1; Pd 2; M = Pt, M' = Pd, 3. N(^)O = o-picolinate, pic; M = Pt, M' = Pt, 4; Pd, 5) are synthesized from the tetranuclear [NBu4]2[{(RF)2Pt(µ-PPh2)2M(µ-Cl)}2] by the elimination of the bridging Cl as AgCl in acetone, and coordination of the corresponding N,O-donor ligand (1, 4, and 5) or connecting the fragments "cis-[(RF)2M(µ-PPh2)2](2-)" and "M'(N(^)O)" (2 and 3). The electrochemical oxidation of the anionic complexes 1-5 occurring under HRMS(+) conditions gave the cations [(RF)2M(µ-PPh2)2M'(N(^)O)](+), presumably endowed with a M(III),M'(III) core. The oxidative addition of I2 to the 8-hydroxyquinolinate complexes 1-3 triggers a reductive coupling between a PPh2 bridging ligand and the N,O-donor chelate ligand with formation of a P-O bond and ends up in complexes of platinum(II) or palladium(II) of formula [(RF)2M(II)(µ-I)(µ-PPh2)M'(II)(P,N-PPh2hq)], M = M' = Pt 7, Pd 8; M = Pt, M' = Pd, 9. Complexes 7-9 show a new Ph2P-OC9H6N (Ph2P-hq) ligand bonded to the metal center in a P,N-chelate mode. Analogously, the addition of I2 to solutions of the o-picolinate complexes 4 and 5 causes the reductive coupling between a PPh2 bridging ligand and the starting N,O-donor chelate ligand with formation of a P-O bond, forming Ph2P-OC6H4NO (Ph2P-pic). In these cases, the isolated derivatives [NBu4][(Ph2P-pic)(RF)Pt(II)(µ-I)(µ-PPh2)M(II)(RF)I] (M = Pt 10, Pd 11) are anionic, as a consequence of the coordination of the resulting new phosphane ligand (Ph2P-pic) as monodentate P-donor, and a terminal iodo group to the M atom. The oxidative addition of I2 to [NBu4][(RF)2Pt(II)(µ-PPh2)2Pt(II)(acac)] (6) (acac = acetylacetonate) also results in a reductive coupling between the diphenylphosphanido and the acetylacetonate ligand with formation of a P-O bond and synthesis of the complex [NBu4][(RF)2Pt(II)(µ-I)(µ-PPh2)Pt(II)(Ph2P-acac)I] (12). The transformations of the starting complexes into the products containing the P-O ligands passes through mixed valence M(II),M'(IV) intermediates which were detected, for M = M' = Pt, by spectroscopic and spectrometric measurements.

Synthesis and reactivity of the unsaturated trinuclear phosphanido complex [(C6F5)2Pt(µ-PPh2)2Pt(µ-PPh2)2Pt(PPh3)].

The reaction of [NBu(4)][(C(6)F(5))(2)Pt(µ-PPh(2))(2)Pt(µ-PPh(2))(2)Pt(O,O-acac)] (48 VEC) with [HPPh(3)][ClO(4)] gives the 46 VEC unsaturated [(C(6)F(5))(2)Pt(1)(µ-PPh(2))(2)Pt(2)(µ-PPh(2))(2)Pt(3)(PPh(3))](Pt(2)-Pt(3)) (1), a trinuclear compound endowed with a Pt-Pt bond. This compound displays amphiphilic behavior and reacts easily with nucleophiles L, yielding the saturated complexes [(C(6)F(5))(2)Pt(II)(µ-PPh(2))(2)Pt(II)(µ-PPh(2))(2)Pt(II)(PPh(3))L] [L = PPh(3) (2), py (3)]. The reaction with the electrophile [Ag(OClO(3))PPh(3)] affords the adduct 1·AgPPh(3), which evolves, even at low temperature, to a mixture in which [(C(6)F(5))(2)Pt(III)(µ-PPh(2))(2)Pt(III)(µ-PPh(2))(2)Pt(II)(PPh(3))(2)](2+)(Pt(III)-Pt(III)) and 2 (plus silver metal) are present. The nucleophilic nature of 1 is also demonstrated through its reaction with cis-[Pt(C(6)F(5))(2)(THF)(2)], which results in the formation of [Pt(4)(µ-PPh(2))(4)(C(6)F(5))(4)(PPh(3))] (4). The structure and NMR features indicate that 1 can be better considered as a Pt(II)-Pt(III)-Pt(I) complex instead of a Pt(II)-Pt(II)-Pt(II) derivative. Theoretical calculations (density functional theory) on similar model compounds are in agreement with the assigned oxidation states of the metal centers. The strong intermetallic interactions resulting in a Pt(2)-Pt(3) metal-metal bond and the respective bonding mechanism were verified by employing a multitude of computational techniques (natural bond order analysis, the Laplacian of the electron density, and localized orbital locator profiles).

Stepwise degradation of trifluoromethyl platinum(II) compounds.

The action of moisture on the homoleptic organoplatinum(II) compound [NBu(4)](2)[Pt(CF(3))(4)] (1) gives rise to the carbonyl derivative [NBu(4)][Pt(CF(3))(3)(CO)] (2), which is itself moisture stable. However, treatment of compound 2 with HCl(aq) results in the formation of [NBu(4)][cis-Pt(CF(3))(2)Cl(CO)] (3), which undergoes degradation of an additional CF(3) group by further treatment with HCl(aq) in large excess, affording [NBu(4)][cis-Pt(CF(3))Cl(2)(CO)] (4). The carbonyl derivatives 2-4 are fairly stable species, in which the CO ligand, however, can be readily extruded by reaction with trimethylamine N-oxide (ONMe(3)). Thus, compound 2 reacts with ONMe(3) in the presence of a number of neutral or anionic ligands affording a series of singly or doubly charged derivatives with the general formulae [NBu(4)][Pt(CF(3))(3)(L)] [L = CNtBu (5), PPh(3) (6), P(o-tolyl)(3) (7), tht (8; tht = tetrahydrothiophene)] and [NBu(4)](2)[Pt(CF(3))(3)X] [X = Cl (9), Br (10), I (11)], respectively. Compound 2 also reacts with ONMe(3) and pyridin-2-thiol (C(5)H(5)NS) giving rise to the five-membered metallacyclic derivative [NBu(4)][Pt(CF(3))(2)(CF(2)NC(5)H(4)S-κC,κS)] (12), which can be viewed as a difluorocarbene species stabilized by intramolecular base coordination. On the other hand, treatment of compound 3 with ONMe(3) in the presence of C(5)H(5)NS yields the four-membered metallacyclic compound [NBu(4)][Pt(CF(3))(2)(NC(5)H(4)S-κN,κS)] (13). The geometries of the metallacycles in compounds 12 and 13 are compared. In the absence of any additional ligand, compound 3 undergoes dimerization producing the dinuclear species [NBu(4)](2)[{Pt(CF(3))(2)}(2)(µ-Cl)(2)] (14). Halide abstraction in the latter compound with AgClO(4) in THF yields the solvento compound cis-[Pt(CF(3))(2)(thf)(2)] (15). The highly labile character of the THF ligands in compound 15 makes this species a convenient synthon of the "cis-Pt(CF(3))(2)" unit.

Formation of P-C bond through reductive coupling between bridging phosphido and benzoquinolinate groups. Isolation of complexes of the Pt(II)/Pt(IV)/Pt(II) sequence.

The rational synthesis of dinuclear asymmetric phosphanido derivatives of palladium and platinum(II), [NBu(4)][(R(F))(2)M(µ-PPh(2))(2)M'(κ(2),N,C-C(13)H(8)N)] (R(F) = C(6)F(5); M = M' = Pt, 1; M = Pt, M' = Pd, 2; M = Pd, M' = Pt, 3; M = M' = Pd, 4), is described. Addition of I(2) to 1-4 gives complexes [(R(F))(2)M(II)(µ-PPh(2))(µ-I)Pd(II){PPh(2)(C(13)H(8)N)}] (M = M' = Pt, 6; M = Pt, M' = Pd, 7; M = M' = Pd, 8; M = Pd, M' = Pt 10) which contain the aminophosphane PPh(2)(C(13)H(8)N) ligand formed through a Ph(2)P/C^N reductive coupling on the mixed valence M(II)-M'(IV) [NBu(4)][(R(F))(2)M(II)(µ-PPh(2))(2)M'(IV)(κ(2),N,C- C(13)H(8)N)I(2)] complexes, which were identified for M(II) = Pd, M'(IV) = Pt (9), and isolated for M(II) = Pt, M'(IV) = Pt (5). Complex 5 showed an unusual dynamic behavior consisting in the exchange of two phenyl groups bonded to different P atoms, as well as a "through space" spin-spin coupling between ortho-F atoms of the pentafluorophenyl rings.

New dicyano cyclometalated compounds containing Pd(II)-Tl(I) bonds as building blocks in 2D extended structures: synthesis, structure, and luminescence studies.

New mixed metal complexes [PdTl(C^N)(CN)(2)] [C^N = 7,8-benzoquinolinate (bzq, 3); 2-phenylpyridinate (ppy, 4)] have been synthesized by reaction of their corresponding precursors (NBu(4))[Pd(C^N)(CN)(2)] [C^N = bzq (1), ppy (2)] with TlPF(6). Compounds 3 and 4 were studied by X-ray diffraction, showing the not-so-common Pd(II)-Tl(I) bonds. Both crystal structures exhibit 2-D extended networks fashioned by organometallic "PdTl(C^N)(CN)(2)" units, each one containing a donor-acceptor Pd(II)-Tl(I) bond, which are connected through additional Tl···N≡C contacts and weak Tl···π (bzq) contacts in the case of 3. Solid state emissions are red-shifted compared with those of the precursors and have been assigned to metal-metal'-to-ligand charge transfer (MM'LCT [d/s σ*(Pd,Tl) → π*(C^N)]) mixed with some intraligand ((3)IL[π(C^N) → π*(C^N)]) character. In diluted solution either at room temperature or 77 K, the Pd-Tl bond is no longer retained as confirmed by mass spectrometry, NMR, and UV-vis spectroscopic techniques.

Luminescent benzoquinolate-isocyanide platinum(II) complexes: effect of Pt⋠⋠⋠Pt and π⋠⋠⋠π interactions on their photophysical properties.

The neutral compounds [Pt(bzq)(CN)(CNR)] (R = tBu (1), Xyl (2), 2-Np (3); bzq = benzoquinolate, Xyl = 2,6-dimethylphenyl, 2-Np = 2-napthyl) were isolated as the pure isomers with a trans-C(bzq),CNR configuration, as confirmed by (13)C{(1)H} NMR spectroscopy in the isotopically marked [Pt(bzq)((13)CN)(CNR)] (R = tBu (1'), Xyl (2'), 2-Np (3')) derivatives (δ(13)C(CN) ≈ 110 ppm; (1) J(Pt,(13)C) ≈ 1425 Hz]. By contrast, complex [Pt(bzq)(C≡CPh)(CNXyl)] (4) with a trans-N(bzq),CNR configuration, has been selectively isolated from [Pt(bzq)Cl(CNXyl)] (trans-N(bzq),CNR) using Sonogashira conditions. X-ray diffraction studies reveal that while 1 adopts a columnar-stacked chain structure with Pt-Pt distances of 3.371(1) Šand significant π⋅⋅⋅π interactions (3.262 Å), complex 2 forms dimers supported only by short Pt⋅⋅⋅Pt (3.370(1) Å) interactions. In complex 4 the packing is directed by weak bzq⋅⋅⋅Xyl and bzq⋅⋅⋅C≡E (C, N) interactions. In solid state at room temperature, compounds 1 and 2 both show a bright red emission (ϕ = 42.1% 1, 57.6% 2). Luminescence properties in the solid state at 77 K and concentration-dependent emission studies in CH(2)Cl(2) at 298 K and at 77 K are also reported for 1-4.

Highly luminescent half-lantern cyclometalated platinum(II) complex: synthesis, structure, luminescence studies, and reactivity.

The half-lantern compound [{Pt(bzq)(µ-C(7)H(4)NS(2)-κN,S)}(2)]·Me(2)CO (1) was obtained by reaction of equimolar amounts of potassium 2-mercaptobenzothiazolate (KC(7)H(4)NS(2)) and [Pt(bzq)(NCMe)(2)]ClO(4). The Pt(II)···Pt(II) separation in the neutral complex [{Pt(bzq)(µ-C(7)H(4)NS(2)-κN,S)}(2)] is 2.910 (2) Å, this being among the shortest observed in half-lantern divalent platinum complexes. Within the complex, the benzo[h]quinoline (bzq) groups lie in close proximity with most C···C distances being between 3.3 and 3.7 Å, which is indicative of significant π-π interactions. The reaction of 1 with halogens X(2) (X(2) = Cl(2), Br(2), or I(2)) proceeds with a two-electron oxidation to give the corresponding dihalodiplatinum(III) complexes [{Pt(bzq)(µ-C(7)H(4)NS(2)-κN,S)X}(2)] (X = Cl 2, Br 3, I 4). Their X-ray structures confirm the retention of the half-lantern structure and the coordination mode of the bzq and the bridging ligand µ-C(7)H(4)NS(2)-κN,S. The Pt-Pt distances (Pt-Pt = 2.6420(3) Å 2, 2.6435(4) Å 3, 2.6690(3) Å 4) are shorter than that in 1 because of the Pt-Pt bond formation. Time dependent-density functional theory (TD-DFT) studies performed on 1 show a formal bond order of 0 between the metal atoms, with the 6p(z) contribution diminishing the antibonding character of the highest occupied molecular orbital (HOMO) and being responsible for an attractive intermetallic interaction. A shortening of the Pt-Pt distance from 2.959 Å in the ground state S(0) to 2.760 Å in the optimized first excited state (T(1)) is consistent with an increase in the Pt-Pt bond order to 0.5. In agreement with TD-DFT calculations, the intense, structureless, red emission of 1 in the solid state and in solution can be mainly attributed to triplet metal-metal-to-ligand charge transfer ((3)MMLCT) [dσ*(Pt-Pt) → π*(bzq)] excited states. The high quantum yields of this emission measured in toluene (44%) and solid state (62%) at room temperature indicate that 1 is a very efficient and stable (3)MMLCT emitter, even in solution. The high luminescence quantum yield of its red emission, added to its neutral character and the thermal stability of 1, make it a potential compound to be incorporated as phosphorescent dopant in multilayer organic light-emitting devices (OLEDs).

Benzoquinolateplatinum(II) complexes as building blocks in the synthesis of Pt-Ag extended structures.

The reaction between (NBu(4))[Pt(bzq)(C(6)F(5))(2)] (1, bzq = 7,8-benzoquinolate) and AgClO(4) in a 1 : 1 molar ratio, in acetone, gives the polymer [{Pt(bzq)(C(6)F(5))(2)}Ag](n) (2). The reaction of 2 with equimolecular amounts of PPh(3) and SC(4)H(8) (tht) produces the bimetallic complexes [{Pt(bzq)(C(6)F(5))(2)}AgL] (L = PPh(3) (3), tht (4)). For L = py, decomposition takes place and [Pt(bzq)(C(6)F(5))py] (5) is obtained. All these complexes have been characterized by X-ray diffraction. The most interesting features of complexes 2-4 is the presence of Pt-Ag bonds, with Pt-Ag distances of ca. 2.75 Å. Besides, the silver centres establish short η(1) bonding interactions with the C(ipso) of the bzq ligands, with distances Ag-C of ca. 2.45 Å. Complex 2 is a one-dimensional infinite chain in which the fragments "Pt(bzq)(C(6)F(5))(2)(-)" and Ag(+) alternate. On the other hand, complexes 1 and 3-5 show intermolecular pairing through π···π interactions between the aromatic rings of the bzq ligand, having interplanar separations of ca. 3.5 Å. Complex 2 dissolves in donor solvents (acetone, THF) as discrete bimetallic solvated fragments [{Pt(bzq)(C(6)F(5))(2)}AgS(n)] (S = solvent), similar to complexes 3 and 4. The persistence of the Pt-Ag bond in 2-4, supported by multinuclear NMR spectroscopy, causes a significant blue-shift in the lowest-lying absorption in relation to 1. This fact is attributed (TD-DFT) to a remarkable modification of the orbitals contributing to the HOMO, which changes the character of the transition from (1)LC/(1)MLCT in 1 to admixture (1)L'LCT/(1)MLCT in the bimetallic complexes. The low energy feature (490-530 nm) of 2 in solid state is attributed to CT from the Pt fragments to the Ag centers. Complexes 2-4 are only emissive in rigid media (solid and glasses). In the solid state, the metallic chain 2 exhibits a bright orange emission (560 nm, 298 K; 590 nm, 77 K), assigned to an excited state involving charge transfer from the platinum fragment with a remarkable contribution of C(6)F(5) (Ar(f)) rings to the Pt-Ag bond ((3)LMM'CT/(3)L'M'CT). However, 3 and 4 exhibit in solid state at 298 K a vibronic band, which is clearly resolved in two close non-equilibrated bands at 77 K in 3, tentatively ascribed to a mixture of (3)MLCT/(3)L'LCT transitions modified by the formation of the Pt-Ag bond. In glassy solution (77 K) 2-4 display a vibronic emission ascribed primarily to (3)LC character.

Behavior of neutral phosphido derivatives of platinum and palladium toward silver centers.

The reaction of the neutral binuclear complexes [(R(F))(2)Pt(µ-PPh(2))(2)M(phen)] (phen = 1,10-phenanthroline, R(F) = C(6)F(5); M = Pt, 1; M = Pd, 2) with AgClO(4) or [Ag(OClO(3))(PPh(3))] affords the trinuclear complexes [AgPt(2)(µ-PPh(2))(2)(R(F))(2)(phen)(OClO(3))] (7a) or [AgPtM(µ-PPh(2))(2)(R(F))(2)(phen)(PPh(3))][ClO(4)] (M = Pt, 8; M = Pd, 9), which display an "open-book" type structure and two (7a) or one (8, 9) Pt-Ag bonds. The neutral diphosphine complexes [(R(F))(2)Pt(µ-PPh(2))(2)M(P-P)] (P-P = 1,2-bis(diphenylphosphino)methane, dppm, M = Pt, 3; M = Pd, 4; P-P = 1,2-bis(diphenylphosphino)ethane, dppe, M = Pt, 5; M = Pd, 6) react with AgClO(4) or [Ag(OClO(3))(PPh(3))], and the nature of the resulting complexes is dependent on both M and the diphosphine. The dppm Pt-Pt complex 3 reacts with [Ag(OClO(3))(PPh(3))], affording a silver adduct 10 in which the Ag atom interacts with the Pt atoms, while the dppm Pt-Pd complex 4 reacts with [Ag(OClO(3))(PPh(3))], forming a 1:1 mixture of [AgPdPt(µ-PPh(2))(2)(R(F))(2)(OClO(3))(dppm)] (11), in which the silver atom is connected to the Pt-Pd moiety through Pd-(µ-PPh(2))-Ag and Ag-P(k(1)-dppm) interactions, and [AgPdPt(µ-PPh(2))(2)(R(F))(2)(OClO(3))(PPh(3))(2)][ClO(4)] (12). The reaction of complex 4 with AgClO(4) gives the trinuclear derivative 11 as the only product. Complex 11 shows a dynamic process in solution in which the silver atom interacts alternatively with both Pd-µPPh(2) bonds. When P-P is dppe, both complexes 5 and 6 react with AgClO(4) or [Ag(OClO(3))(PPh(3))], forming the saturated complexes [(PPh(2)C(6)F(5))(R(F))Pt(µ-PPh(2))(µ-OH)M(dppe)][ClO(4)] (M = Pt, 13; Pd, 14), which are the result of an oxidation followed by a PPh(2)/C(6)F(5) reductive coupling. Finally, the oxidation of trinuclear derivatives [(R(F))(2)Pt(II)(µ-PPh(2))(2)Pt(II)(µ-PPh(2))(2)Pt(II)L(2)] (L(2) = phen, 15; L = PPh(3), 16) by AgClO(4) results in the formation of the unsaturated 46 VEC complexes [(R(F))(2)Pt(III)(µ-PPh(2))(2)Pt(III)(µ-PPh(2))(2)Pt(II)L(2)][ClO(4)](2) (17 and 18, respectively) which display Pt(III)-Pt(III) bonds.

Efficient and stereoselective syntheses of isomeric trifluoromethyl-platinum(IV) chlorides.

The homoleptic, square-planar trifluoromethylplatinate(II) compound [NBu(4)](2)[Pt(CF(3))(4)] (1) reacts with SOCl(2) undergoing oxidative addition of a S-Cl bond to give the octahedral species [NBu(4)](2)[trans-Pt(CF(3))(4)Cl(SOCl)] (4), that contains the unusual chlorosulfinyl ligand. Compound 4 readily evolves into the dichloro-derivative [NBu(4)](2)[cis-Pt(CF(3))(4)Cl(2)] (2), whereby the "Pt(CF(3))(4)" unit undergoes a stereochemical rearrangement from an initial square-planar (equatorial) geometry to a final sawhorse disposition within the global Pt octahedral environment. Compound 2 is more reactive than the corresponding [NBu(4)](2)[trans-Pt(CF(3))(4)Cl(2)] (3) stereoisomer and thus affords the trichloro-derivative [NBu(4)](2)[fac-Pt(CF(3))(3)Cl(3)] (5) by treatment with the stoichiometrically required amount of HCl(aq). Stereoisomer [NBu(4)](2)[mer-Pt(CF(3))(3)Cl(3)] (6) has been obtained by oxidative addition of Cl(2) to the organoplatinum(II) precursor [NBu(4)](2)[Pt(CF(3))(3)Cl]. All the synthetic procedures described here proceed in high yields and in a stereoselective manner. The optical properties of the cis-/trans-[Pt(CF(3))(4)Cl(2)](2-) and fac-/mer-[Pt(CF(3))(3)Cl(3)](2-) diastereomeric couples (diffuse reflectance) as well as the solid-state geometries of the latter couple (single-crystal X-ray diffraction methods) are conveniently compared.

Highly trifluoromethylated platinum compounds.

The homoleptic, square-planar organoplatinum(II) compound [NBu(4)](2) [Pt(CF(3))(4)] (1) undergoes oxidative addition of CF(3) I under mild conditions to give rise to the octahedral organoplatinum(IV) complex [NBu(4)](2) [Pt(CF(3))(5)I] (2). This highly trifluoromethylated species reacts with Ag(+) salts of weakly coordinating anions in Me(2)CO under a wet-air stream to afford the aquo derivative [NBu(4)][Pt(CF(3))(5) (OH(2))] (4) in around 75% yield. When the reaction of 2 with the same Ag(+) salts is carried out in MeCN, the solvento compound [NBu(4) ][Pt(CF(3))(5)(NCMe)] (5) is obtained in around 80% yield. The aquo ligand in 4 as well as the MeCN ligand in 5 are labile and can be cleanly replaced by neutral and anionic ligands to furnish a series of pentakis(trifluoromethyl)platinate(IV) compounds with formulae [NBu(4)][Pt(CF(3))(5) (L)] (L=CO (6), pyridine (py; 7), tetrahydrothiophene (tht; 8)) and [NBu(4)](2) [Pt(CF(3))(5)X] (X=Cl (9), Br (10)). The unusual carbonyl-platinum(IV) derivative [NBu(4)][Pt(CF(3))(5) (CO)] (6) is thermally stable and has a ν(CO) of 2194 cm(-1). The crystal structures of 2⋅CH(2)Cl(2), 5, [PPh(4) ][Pt(CF(3))(5)(CO)] (6'), and 7 have been established by X-ray diffraction methods. Compound 2 has shown itself to be a convenient entry to the chemistry of highly trifluoromethylated platinum compounds. To the best of our knowledge, compounds 2 and 4-10 are the organoelement compounds with the highest CF(3) content to have been isolated and adequately characterized to date.

Pt-Ag clusters and their neutral mononuclear Pt(II) starting complexes: structural and luminescence studies.

The mononuclear complexes [Pt(bzq)(S^S)] [S^S = pyrrolidinedithiocarbamate (pdtc 1), dimethyldithiocarbamate (dmdtc 2)] were prepared by reaction of [Pt(bzq)(NCMe)(2)]ClO(4) with an equimolecular amount of [NH(4)(pdtc)] and [Na(dmdtc)·2H(2)O] respectively in MeOH. Reactions of 1 and 2 with AgClO(4) in 1 : 1 and 2 : 1 molar ratios rendered the heteropolinuclear compounds [{Pt(bzq)(S^S)Ag}(2)](ClO(4))(2) (S^S = pdtc 3, dmdtc 4) and [{Pt(bzq)(S^S)}(2)Ag](ClO(4)) (S^S = pdtc 5, dmdtc 6) respectively. The X-ray studies on single crystals of 3 and 4 showed that both consist of tetranuclear [Pt(2)Ag(2)] clusters with the Pt-Ag and the Ag-Ag distances in the range of those corresponding to Pt-Ag dative bonds and argentophilic interactions. In 3 the tetranuclear [Pt(2)Ag(2)] clusters are connected into infinite polymeric chains by Pt···Pt metallophilic interactions (Pt···Pt = 3.1890(7) Å). The X-ray study on a single crystal of 5 showed that it is a polymer based on trinuclear [Pt(2)Ag] clusters containing two unsupported Pt-Ag dative bonds and connected by Ag-S bonds in such a way that the "Pt-Ag-S-Pt-Ag-S" atoms draw a zigzag polymeric chain. TD-DFT calculations carried out for 1 indicate that the lowest energy absorption band in CH(2)Cl(2) can be described as a mixture of (1)MLCT, (1)IL and (1)L'LCT transitions. Powdered samples of 1 at 298 K and 77 K show a green-yellow emission band coming mainly from a (3)LC excited state. However complex 2 shows "luminescence thermochromism": the colour of its luminescence changes from green-yellow at 77 K to orange-red at 298 K. The emission of the Pt-Ag clusters, 3-6, in the solid state, are due to excimeric (3)ππ and/or (3)MMLCT (dσ* →π*) low-lying excited states, indicating that the presence of silver in the clusters makes the "Pt(bzq)(S^S)" fragments interact to a large extent through Pt···Pt and/or π-π interactions. Solid 3 is a highly selective vapochromic compound towards acetonitrile although this behaviour is not fully reversible.

Synthesis, dynamic behavior, and reactivity of new unsaturated heterotrinuclear 46 valence electron complexes.

The reaction of [NBu(4)](2)[(C(6)F(5))(2)Pt(µ-PPh(2))(2)Pd(µ-PPh(2))(2)Pt(C(6)F(5))(2)] (1a) with [AgPPh(3)](+) results in the oxidation of two bridging diphenylphosphanides to give the 46e species [(PPh(3))(C(6)F(5))(2)Pt(2)(µ-P(2)Ph(2))Pd(µ-PPh(2))(µ-Ph(2)P(4)-P(3)Ph(2))Pt(1)(C(6)F(5))(2)] (3). Complex 3 displays two tetracoordinated terminal platinum centers and a central Pd atom that is bonded to three P atoms and that completes its coordination sphere by a rather long (3.237 Å) dative Pt(2) → Pd bond. Complex 3 is also obtained when [(R(F))(2)Pt(µ-PPh(2))Pd(µ-PPh(2))(µ-Ph(2)P-PPh(2))Pt(R(F))(2)] (2) is reacted with PPh(3). Analogously, the addition of PPh(2)Et, CO or pyridine to 2 affords the 46e complexes of general formula [(L)(C(6)F(5))(2)Pt(2)(µ-P(2)Ph(2))Pd(µ-PPh(2))(µ-Ph(2)P(4)-P(3)Ph(2))Pt(1)(C(6)F(5))(2)] (L = PPh(2)Et, 4; L = CO, 6; L = pyridine, 7). The geometry around Pt(2) is determined by the bulkiness of L bonded to Pt. Thus, in complexes 3 (L = PPh(3)) and 4 (L = PPh(2)Et), the ligand L occupies the trans position with respect to µ-P(2), and in 6 (L = CO), the ligand L occupies the cis position with respect to µ-P(2). Interestingly, for 7 (L = py), both isomers 7-trans and 7-cis, could be isolated. Although 4 did not react with an excess of PPh(2)Et, the reaction with the less sterically demanding CH(3)CN ligand resulted in the opening of the Pt(2)-P(2)-Pd cycle with formation of the saturated 48e species [(PPh(2)Et)(C(6)F(5))(2)Pt(µ-PPh(2))Pd(MeCN)(µ-PPh(2))(µ-Ph(2)P-PPh(2))Pt(C(6)F(5))(2)] (8). The saturated 48e complex [(CO)(C(6)F(5))(2)Pt(µ-PPh(2))Pd(MeCN)(µ-PPh(2))(µ-Ph(2)P-PPh(2))Pt(C(6)F(5))(2)] (9) was obtained by acetonitrile addition to 6. Beside the hindered rotation of the pentafluorophenyl groups and a flip-flop motion of the Pd-P-Pt(1)-P-P ring observed at low T, a rotation about the Pt(2)-P(2) bond and a P-C oxidative addition/reductive elimination process occur for 3 and 4 at room temperature. A "through-space" (19)F-(31)P spin-spin coupling between an ortho-F and the P(4) is observed for complexes 3 and 4, having the C(6)F(5) groups bonded to Pt(2) in mutually trans position. The XRD structures of complexes 3, 6, 7-trans, 7-cis, 8, and 9 are described.

Synthesis and characterization of neutral and anionic carbonyl derivatives of palladium(II).

The action of CO on the solvento-complexes cis-[PdR2(thf)2] [R = C6F5 (1), C6Cl5 (2)] at low temperature gives cis-[PdR2(CO)2] [R = C6F5 (3), C6Cl5 (4)] in good yield by simple replacement of the highly labile thf molecules. These are rare cases of Pd(II) dicarbonyl compounds, whose characterization relies on spectroscopic and analytic data. The crystal structure of the square-planar platinum homologue cis-[Pt(C6Cl5)2(CO)2] is also presented. CO can split the double bridging-system in the dinuclear species [{PdR2}2(mu-X)2]2- giving the homologous series of anionic monocarbonyl Pd(II) derivatives with formula [cis-PdR2X(CO)]- (5-10: R = C6F5, C6Cl5; X = Cl, Br, I), which were isolated (except for the R = C6F5 and X = I) and suitably characterized. Characterization includes the crystal and molecular structure of [PPh3Me][cis-Pd(C6F5)2Br(CO)] (6'). The anionic species [NBu4][cis-Pd(C6F5)2Cl(CO)] (5) reacts with neutral cis-[Pd(C6F5)2(CO)2] (3) under CO extrusion, affording the dinuclear derivative [NBu4][{Pd(C6F5)2(CO)}2(mu-Cl)] (11), which contains a single unsupported halide bridge (X-ray diffraction). Complex 11 can be considered as modelling a possible intermediate step in intermolecular CO substitution reactions that are easily undergone by Pd(II) halo carbonyl species.

Structural and luminescence studies on pi...pi and Pt...Pt interactions in mixed chloro-isocyanide cyclometalated platinum(II) complexes.

[Pt(bzq)Cl(CNR)] [bzq = benzoquinolinate; R = tert-butyl ((t)Bu 1), 2-6-dimethylphenyl (Xyl 2), 2-naphthyl (2-Np 3)] complexes have been synthesized and structurally and photophysically characterized. 1 was found to co-crystallize in two distinct pseudopolymorphs: a red form, which exhibits an infinite 1D-chain ([1](infinity)) and a yellow form, which contains discrete dimers ([1](2)), both stabilized by interplanar pi...pi (bzq) and short Pt...Pt bonding interactions. Complex 3, generated through the unexpected garnet-red double salt isomer [Pt(bzq)(CN-2-Np)(2)][Pt(bzq)Cl(2)] 4, crystallizes as yellow Pt...Pt dimers ([3](2)), while 2 only forms pi...pi (bzq) contacting dimers. Their electronic absorption and luminescence behaviors have been investigated. According to Time-Dependent Density Functional Theory (TD-DFT) calculations, the lowest-lying absorption (CH(2)Cl(2)) has been attributed to combined (1)ILCT and (1)MLCT/(1)ML'CT (L = bzq, L' = CNR) transitions, the latter increasing from 1 to 3. In solid state, while the yellow form [1](2) exhibits a green (3)MLCT unstructured emission only at 77 K, the 1-D form [1](infinity) displays a characteristic low-energy red emission (672 nm, 298 K; 744 nm, 77 K) attributed to a mixed (3)MMCT [d(sigma*)-->p(sigma)]/(3)MMLCT [dsigma*(M(2))-->sigma(pi*)(bzq)] excited state. However, upon exposure to standard atmospheric conditions, [1](infinity) shows an irreversible change to an orange-ochre solid, whose emissive properties are similar to those of the crude 1. Complexes 2 and 3 (77 K) exhibit a structured emission from discrete fragments ((3)LC/(3)MLCT), whereas the luminescence of the garnet-red salt 4 is dominated by a low energy emission (680 nm, 298 K; 730 nm, 77 K) arising from a (3)MMLCT excited state. Solvent (CH(2)Cl(2), toluene, 2-MeTHF and CH(3)CN) and concentration-dependent emission studies at 298 K and at 77 K are also reported for 1-3. In CH(2)Cl(2) solution, the low phosphorescent emission band is ascribed to bzq intraligand charge transfer (3)ILCT mixed with metal-to-ligand (L = bzq, L' = CNR) charge transfer (3)MLCT/(3)ML'CT character with the Pt to CNR contribution increasing from 1 to 3, according to computational studies.