Twisted and Disconnected Chains: Flexible Linear Tetracuprous Arrays and a Decanuclear CuI Cluster as Blue- and Green/Yellow-Light Emitters.

Defined arrays of transition metal ions embedded in tailored polydentate ligand scaffolds allow for a systematic design of their physical properties. Such molecular strings of closed-shell transition metal centers are particularly interesting for Group 11 metal ions in the oxidation state +1 if they undergo metallophilic d10···d10 contact interactions since these clusters are oftentimes efficient photoluminescence (PL) emitters. Copper is particularly attractive as a sustainable earth-abundant coinage metal source and because of the ability of several CuI complexes to serve as powerful thermally activated delayed fluorescence (TADF) emitters in molecular/organic light-emitting devices (OLEDs). Our combined synthetic, crystallographic, photophysical, and computational study describes a straight tetracuprous array possessing a centrally disconnected CuI2···CuI2 chain and a continuous helically bent CuI4 complex. This molecular helix undergoes a facile rearrangement in diethyl ether solution, yielding an unprecedented nanosized CuI10 cluster (2.9 × 2.0 nm) upon crystallization. All three clusters show either bright blue phosphorescence, TADF, or green/yellow multiband phosphorescence with quantum yields between 6.5 and 67%, which is persistent under hydrostatic pressure up to 30 kbar. Temperature-dependent PL investigations in combination with time-dependent density-functional theory (TD-DFT) calculations and void space analyses of the crystal packings complement a comprehensive correlation between the molecular structures and photoluminescence properties.

Syntheses, homeomorphic and configurational isomerizations, and structures of macrocyclic aliphatic dibridgehead diphosphines; molecules that turn themselves inside out.

The diphosphine complexes cis- or trans-[upper bond 1 start]PtCl2(P((CH2) n )3P[upper bond 1 end]) (n = b/12, c/14, d/16, e/18) are demetalated by MC[triple bond, length as m-dash]X nucleophiles to give the title compounds (P((CH2) n )3)P (3b-e, 91-71%). These "empty cages" react with PdCl2 or PtCl2 sources to afford trans-[upper bond 1 start]MCl2(P((CH2) n )3P[upper bond 1 end]). Low temperature 31P NMR spectra of 3b and c show two rapidly equilibrating species (3b, 86 : 14; 3c, 97 : 3), assigned based upon computational data to in,in (major) and out,out isomers. These interconvert by homeomorphic isomerizations, akin to turning articles of clothing inside out (3b/c: ΔH ‡ 7.3/8.2 kcal mol-1, ΔS ‡ -19.4/-11.8 eu, minor to major). At 150 °C, 3b, c, e epimerize to (60-51) : (40-49) mixtures of (in,in/out,out) : in,out isomers, which are separated via the bis(borane) adducts 3b, c, e·2BH3. The configurational stabilities of in,out-3b, c, e preclude phosphorus inversion in the interconversion of in,in and out,out isomers. Low temperature 31P NMR spectra of in,out-3b, c reveal degenerate in,out/out,in homeomorphic isomerizations (ΔG ‡ Tc 12.1, 8.5 kcal mol-1). When (in,in/out,out)-3b, c, e are crystallized, out,out isomers are obtained, despite the preference for in,in isomers in solution. The lattice structures are analyzed, and the D 3 symmetry of out,out-3c enables a particularly favorable packing motif. Similarly, (in,in/out,out)-3c, e·2BH3 crystallize in out,out conformations, the former with a cycloalkane solvent guest inside.

Non-conventional hydrogen bonding and dispersion forces that support embedding mesitylgold into a tailored bis(amidine) framework.

A bis(amidine) ligand operates as a molecular lock for two AuMes fragments. The resulting complex retains a flexible double macrocycle with two non-conventional N-H⋯Cipso hydrogen bonds and distinct intramolecular dispersion forces. Instead of unfolding of the double-ring structure through bond rupture in solution, a conformational ring inversion is observed.

Ethylene-Bridged Hexadentate Bis(amidines) and Bis(amidinates) with Variable Binding Sites.

Hexadentate bis(amidines) form versatile networks of hydrogen bonds both in solid state and solution, as revealed by X-ray crystallography, IR, and NMR spectroscopy. Moreover, the corresponding bis(amidinates) produce blue and green emissions in THF solution. Tethered tetradentate bis(amidines) have emerged in coordination chemistry, enantioselective catalysis, as building blocks for polyfunctional heterocycles, and in photoluminescent materials. The next generation of flexible bis(amidine)/bis(amidinate) platforms with up to six N-donor sites has now been established.

Linear Copper Complex Arrays as Versatile Molecular Strings: Syntheses, Structures, Luminescence, and Magnetism.

The defined linear arrangement of metal atoms in discrete coordination complexes or polymers is still one of the most intriguing challenges in synthetic chemistry. These chain arrangements are of fundamental importance, because of their potential applications as molecular wires and single molecule magnets (SMM) in microelectronic devices on a molecular scale. Oligonuclear Group 11 metal complexes with suitable bridging ligands, specifically those that are based on copper as the first choice of a cheap precursor coinage metal, are of particular interest in this regard. This is due to the superior luminescence properties of these linear clusters that often show d10 ⋅⋅⋅d10 interactions in their molecular structures. The combination of CuI with heavier coinage metal ions results in tunable emissive arrays that are also stimuli-responsive. Thus, both linear multinuclear CuI and linear heteropolymetallic CuI /AgI as well as CuI /AuI clusters are excellent candidates for applications in molecular/organic light-emitting devices (OLEDs). Alternatively, paramagnetic multinuclear cupric arrays are prominent as potential molecular wires with enhanced magnetic properties through multiple coupled d9 centers. This Review covers the whole range of linear multinuclear assemblies of cuprous and cupric ions in complexes and coordination polymers, their syntheses, photophysical behavior, and magnetic properties. Moreover, recent advances in the rapidly progressing field of hetero-CuI /AgI and CuI /AuI molecular strings are also discussed.

Non-metal-templated approaches to bis(borane) derivatives of macrocyclic dibridgehead diphosphines via alkene metathesis.

Two routes to the title compounds are evaluated. First, a ca. 0.01 M CH2Cl2 solution of H3B·P((CH2)6CH=CH2)3 (1·BH3) is treated with 5 mol % of Grubbs' first generation catalyst (0 °C to reflux), followed by H2 (5 bar) and Wilkinson's catalyst (55 °C). Column chromatography affords H3B·P(n-C8H17)3 (1%), H3B·P((CH2)13CH2)(n-C8H17) (8%; see text for tie bars that indicate additional phosphorus-carbon linkages, which are coded in the abstract with italics), H3B·P((CH2)13CH2)((CH2)14)P((CH2)13CH2)·BH3 (6·2BH3, 10%), in,out-H3B·P((CH2)14)3P·BH3 (in,out-2·2BH3, 4%) and the stereoisomer (in,in/out,out)-2·2BH3 (2%). Four of these structures are verified by independent syntheses. Second, 1,14-tetradecanedioic acid is converted (reduction, bromination, Arbuzov reaction, LiAlH4) to H2P((CH2)14)PH2 (10; 76% overall yield). The reaction with H3B·SMe2 gives 10·2BH3, which is treated with n-BuLi (4.4 equiv) and Br(CH2)6CH=CH2 (4.0 equiv) to afford the tetraalkenyl precursor (H2C=CH(CH2)6)2(H3B)P((CH2)14)P(BH3)((CH2)6CH=CH2)2 (11·2BH3; 18%). Alternative approaches to 11·2BH3 (e.g., via 11) were unsuccessful. An analogous metathesis/hydrogenation/chromatography sequence with 11·2BH3 (0.0010 M in CH2Cl2) gives 6·2BH3 (5%), in,out-2·2BH3 (6%), and (in,in/out,out)-2·2BH3 (7%). Despite the doubled yield of 2·2BH3, the longer synthesis of 11·2BH3 vs 1·BH3 renders the two routes a toss-up; neither compares favorably with precious metal templated syntheses.

Homeomorphic Isomerization as a Design Element in Container Molecules; Binding, Displacement, and Selective Transport of MCl2 Species (M = Pt, Pd, Ni).

The dibridgehead diphosphine ((CH2)14)3 P (1) can rapidly turn inside-out (homeomorphic isomerization) to give a mixture of in,in and out,out isomers. The exo directed lone pairs in the latter are able to scavenge Lewis acidic MCl2; cagelike adducts of the in,in isomer, trans- Cl2(P((CH2)14)3 P) (M = 2/Pt, 3/Pd, 4/Ni), then form. The NiCl2 unit in 4 may be replaced by PtCl2 or PdCl2, but 2 and 3 do not give similar substitutions. U-tubes are charged with CH2Cl2 solutions of 1 (lower phase), an aqueous solution of K2MCl4 (charging arm; M = Pt, Pd), and an aqueous solution of excess KCl (receiving arm). The MCl2 units are then transported to the receiving arm until equilibrium is reached (up to 22 d). When the receiving arm is charged with KCN, transport is much faster (ca. 100 h) and higher K2MX4 equilibrium ratios are obtained (≥96≤4). Analogous experiments with K2PtCl4/K2PdCl4 mixtures show PdCl2 transport to be more rapid. A similar diphosphine with longer methylene chains, P((CH2)18)3P, is equally effective. No transport occurs in the absence of 1, and other diphosphines or monophosphines assayed give only trace levels.

Highly Luminescent Linear Complex Arrays of up to Eight Cuprous Centers.

Linearly arranged metal atoms that are embedded in discrete molecules have fascinated scientists across various disciplines for decades; this is attributed to their potential use in microelectronic devices on a submicroscopic scale. Luminescent oligonuclear Group 11 metal complexes are of particular interest for applications in molecular light-emitting devices. Herein, we describe the synthesis and characterization of a rare, homoleptic, and neutral linearly arranged tetranuclear Cu(I) complex that is helically bent, thus representing a molecular coil in the solid state. This tetracuprous arrangement dimerizes into a unique octanuclear assembly bearing a linear array of six Cu(I) centers with two additional bridging cuprous ions that constitute a central pseudo-rhombic Cu(I) 4 cluster. The crystal structure determinations of both complexes reveal close d(10) ⋅⋅⋅d(10) contacts between all cuprous ions that are adjacent to each other. The dynamic behavior in solution, DFT calculations, and the luminescence properties of these remarkable complexes are also discussed.

Steric control of the in/out sense of bridgehead substituents in macrobicyclic compounds: isolation of new "crossed chain" variants of in/out isomers.

Isomers of the cage like dibridgehead diphosphine P((CH2)14)3P (1) are treated with Ph3PAu(2,6-C6H3(Trip)2) (2 equiv.; Trip = 2,4,6-C6H2(iPr)3). With out,out-1, workup gives out,out-1·(Au(2,6-C6H3(Trip)2))2 (46%), as confirmed by a crystal structure. With in,out-1, crystallization affords not in,out-1·(Au(2,6-C6H3(Trip)2))2, but rather an out,out isomer in which one of the (CH2)14 segments threads through the macrocycle formed by the other two. Implications for mechanisms of interconversion of in,out isomers are analyzed.

Gyroscope-like molecules consisting of PdX2/PtX2 rotators within three-spoke dibridgehead diphosphine stators: syntheses, substitution reactions, structures, and dynamic properties.

Threefold intramolecular ring-closing metatheses of trans-[MCl2(P{(CH2)(m)CH=CH2}3)2] are effected with Grubbs' catalyst. Following hydrogenation catalyzed by [RhCl(PPh3)3], the title complexes trans-[MCl2(P((CH2)n)3P)] (n=2m+2; M/n=Pt/14, 4 c; Pt/16, 4 d; Pt/18, 4 e; Pd/14, 5 c; Pd/18, 5 e) and sometimes isomers partly derived from intraligand metathesis, trans-[MCl2{P(CH2)n(CH2)n}P(CH2)n)] (4'c-e, 5'e), are isolated. These react with LiBr, NaI, and KCN to give the corresponding MBr2, MI2, and M(CN)2 species (58-99%). (13)C NMR data show that the MX2 moieties rapidly rotate within the diphosphine cage on the NMR timescale, even at -120 °C. The reaction of 4 c and KSCN gives separable Pt(NCS)2 and Pt(NCS)(SCN) adducts (13 c, 28%; 14 c, 20%), and those of 4 c,e and Ph2Zn give PtPh2 species (15 c, 61%; 15 e, 90%). (13)C NMR spectra of 13 c-15 c show two sets of CH2 signals (ca. 2:1 intensity ratios), indicating that MX2 rotation is no longer rapid. Reactions of 4 c or 4'c and excess NaC≡CH afford the free diphosphines P{(CH2)14}3P (91%) and (CH2)14P(CH2)14P(CH2)14 (90%). The latter has been crystallographically characterized as a bis(BH3) adduct. The crystal structures of eight complexes with P(CH2)14P linkages (PtCl2, PtBr2, PtI2, Pt(NCS)2, PtPh2, PdCl2, PdBr2, PdI2) and 15 e have been determined, and intramolecular distances analyzed with respect to MX2 rotation. The conformations of the (CH2)14 moieties and features of the crystal lattices are also discussed.

Oligonuclear homoleptic copper(I) pyrazolates with multinucleating ligand scaffolds: high structural diversity in solid-state and solution.

The synthesis of three pyrazole-based, potentially binucleating ligands 3,5-bis(R(1)N(CH(3))CH(2))-4-R(2)pyrazole (L(1)H: R(1) = pyridyl-2-methyl-, R(2) = Ph; L(2)H: R(1) = 8-quinolyl-, R(2) = H; L(3)H: R(1) = 8-quinolyl-, R(2) = Ph) is described. Reaction of L(1-3)H with 1 equiv. of mesitylcopper affords oligonuclear homoleptic complexes of the type [CuL](n) (1-3). The single crystal X-ray structure of 2 shows a tetranuclear assembly of linear coordinated copper(I)-centers bridged by pyrazolato ligands that alternate above and below the Cu(4) plane, with additional weak interactions from some of the ligand side arms. As the single crystal X-ray structure of 3 reveals, phenyl substitution at the 4-position of the pyrazolato framework leads to significant structural modification of the Cu(4) array, giving a rhombical tetranuclear complex with two linear coordinated copper(I) centers that exhibit a short intramolecular Cu...Cu contact (2.8212(10) A) and two peripheral copper(I) centers in a distorted tetrahedral coordination mode. Thus, 3 represents a very rare example of an inorganic pyrazolato cuprate which can also be viewed as a partly rearranged structural isomer of 2. Furthermore, the crystal lattice of 3 shows an extended network of intra- and intermolecular pi-pi stacking interactions between the aromatic rings. In solution, 1-3 each form two types of oligomers a and b that slowly (<1 s(-1)) equilibrate at room temperature. Using Diffusion Ordered Spectroscopy (DOSY) and variable temperature (1)H NMR spectroscopy it can be shown that a and b correspond to a tetrameric and a (planar) trimeric species. Coordination of the pyridyl/quinolyl side arms that is observed in the solid state seems to be only transient in solution.

An unusually stable octanuclear sigma-mesityl-bridged mu4-oxo-copper(I) complex encapsulated by a pyrazolate-based compartmental ligand scaffold.

A new compartmental pyrazole-derived chelating ligand, four equivalents of mesitylcopper and stoichiometric amounts of dioxygen lead to the formation of a remarkably stable organometallic framework that can be described as a heteroleptic O-centered cuprate anion [(MesCu(I))(4)(mu(4)-O)](2-) linked via sigma-mesityl-bridges to two surrounding binuclear Cu(I)-pyrazolate clamps.