A neutral diphosphene radical: synthesis, electronic structure and white phosphorus activation.

(ClImDipp)P-P(Dipp)˙ (1˙), a rare example of a neutral, mixed substituted diphosphene radical, has been prepared by reduction of (ClImDipp)PP(Dipp)[OTf] (2[OTf]) and (ClImDipp)PP(Cl)(Dipp) (3) with cobaltocene (CoCp2) (ClImDipp = 4,5-dichloro-1,3-bis(1,3-diisopropylphenyl)-imidazol-2-yl, Dipp = 2,6-diisopropylphenyl). Radical compound 1˙ readily activates white phosphorus (P4), resulting in the formation of an intriguing octaphosphane butterfly compound P8(ClImDipp)2(Dipp)2 (4).

Visible-Light-Triggered Photoswitching of Diphosphene Complexes.

Although diphosphene transition metal complexes are known to undergo E to Z isomerization upon irradiation with UV light, their potential for photoswitching has remained poorly explored. In this study, we present diphosphene complexes capable of reversible photoisomerizations through haptotropic rearrangements. The compounds [(2-κ2 P,κ6 C)Mo(CO)2 ][OTf] (3 a[OTf]), [(2-κ2 P,κ6 C)Fe(CO)][OTf] (3 b[OTf]), and [(2-κ2 P)Fe(CO)4 ][OTf] (4[OTf]) were prepared using the triflate salt [(LC )P=P(Dipp)][OTf] (2[OTf) as a precursor (LC =4,5-dichloro-1,3-bis(2,6-diisiopropylphenyl)-imidazolin-2-yl; Dipp=2,6-diisiopropylphenyl, OTf=triflate). Upon exposure to blue or UV light (λ=400 nm, 470 nm), the initially red-colored η2 -diphosphene complexes 3 a,b[OTf] readily undergo isomerization to form blue-colored η1 -complexes [(2-κ1 P,κ6 C)M(CO)n ][OTf] (5 a,b[OTf]; a: M=Mo, n=2; b: M=Fe, n=1). This haptotropic rearrangement is reversible, and the (κ2 P,κ6 C)-coordination mode gradually reverts back upon dissolution in coordinating solvents or more rapidly upon exposure to yellow or red irradiation (λ=590 nm, 630 nm). The electronic reasons for the reversible visible-light-induced photoswitching observed for 3 a,b[OTf] are elucidated by DFT calculations. These calculations indicate that the photochromic isomerization originates from the S1 excited state and proceeds through a conical intersection.

Formation of a Hexaphosphido Cobalt Complex through P-P Condensation.

The reaction between diphosphorus derivatives [(Cl ImDipp )P2 (Dipp)]OTf (1[OTf]) and [(Cl ImDipp )P2 (Dipp)Cl] (1[Cl]) with the cyclotetraphosphido cobalt complex [K(18c-6)][(PHDI)Co(η4 -cyclo-P4 )] (2) leads to the formation of complex [(PHDI)Co{η4 -cyclo-P6 (Dipp)(Cl ImDipp )}] (3), which features an unusual hexaphosphido ligand [Cl ImDipp =4,5-dichloro-1,3-bis(2,6-diisopropylphenyl)imidazol-2-yl, Dipp=2,6-diisopropylphenyl, 18c-6=18-crown-6, PHDI=bis(2,6-diisopropylphenyl)phenanthrene-9,10-diimine]. Complex 3 was obtained as a crystalline material with a moderate yield at low temperature. Upon exposure to ambient temperature, compound 3 slowly transforms into two other compounds, [K(18c-6)][(PHDI)Co(η4 -P7 Dipp)] (4) and [(PHDI)Co{cyclo-P5 (Cl ImDipp )}] (5). The novel complexes 3-5 were characterized using multinuclear NMR spectroscopy and single-crystal X-ray diffraction. To shed light on the formation of these compounds, a proposed mechanism based on 31 P NMR monitoring studies is presented.

An unusual Ni2Si2P8 cluster formed by complexation and thermolysis.

[LSi(η2-P4)] (L = CH[C(Me)N(Dipp)][C(CH2)N(Dipp)], Dipp = 2,6-diisopropylphenyl) forms well-defined 1 : 1 and 2 : 1 complexes with N-heterocyclic carbene nickel fragments. The cluster compound [(IDipp)Ni2P8(SiL)2] (IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) is selectively formed by thermolysis of the complex [(IDipp)Ni(µ-η2:2-P4)SiL].

P-P Condensation and P-N/P-P Bond Metathesis: Facile Synthesis of Cationic Tri- and Tetraphosphanes.

[LC R P((PhP)2 C2 H4 )][OTf] (4 a,b[OTf]) and [LC iPr P(PPh2 )2 ][OTf] (5 b[OTf]) were prepared from the reaction of imidazoliumyl-substituted dipyrazolylphosphane triflate salts [LC R P(pyr)2 ][OTf] (3 a,b[OTf]; a: R=Me, b=iPr; LC R =1,3-dialkyl-4,5-dimethylimidazol-2-yl; pyr=3,5-dimethylpyrazol-1-yl) with the secondary phosphanes PhP(H)C2 H4 P(H)Ph) and Ph2 PH. A stepwise double P-N/P-P bond metathesis to catena-tetraphosphane-2,3-diium triflate salt [(Ph2 P)2 (LC Me P)2 ][OTf]2 (7 a[OTf]2 ) is observed when reacting 3 a[OTf] with diphosphane P2 Ph4 . The coordination ability of 5 b[OTf] was probed with selected coinage metal salts [Cu(CH3 CN)4 ]OTf, AgOTf and AuCl(tht) (tht=tetrahydrothiophene). For AuCl(tht), the helical complex [{(Ph2 PPLC iPr )Au}4 ][OTf]4 (9[OTf]4 ) was unexpectedly formed as a result of a chloride-induced P-P bond cleavage. The weakly coordinating triflate anion enables the formation of the expected copper(I) and silver(I) complexes [(5 b)M(CH3 CN)3 ][OTf]2 (M=Cu, Ag) (10[OTf]2 , 11[OTf]2 ).

Functionalization of Pentaphosphorus Cations by Complexation.

The chemistry of polyphosphorus cations has rapidly developed in recent years, but their coordination behavior has remained mostly unexplored. Herein, we describe the reactivity of [P5 R2 ]+ cations with cyclopentadienyl metal complexes. The reaction of [CpAr Fe(µ-Br)]2 (CpAr =C5 (C6 H4 -4-Et)5 ) with [P5 R2 ][GaCl4 ] (R=iPr and 2,4,6-Me3 C6 H2 (Mes)) afforded bicyclo[1.1.0]pentaphosphanes (1-R, R=iPr and Mes), showing an unsymmetric "butterfly" structure. The same products 1-R were formed from K[CpAr ] and [P5 R2 ][GaCl4 ]. The cationic complexes [CpAr Co(η4 -P5 R2 )][GaCl4 ] (2-R[GaCl4 ], R=iPr and Cy) and [(CpAr Ni)2 (η3:3 -P5 R2 )][GaCl4 ] (3-R[GaCl4 ]) were obtained from [P5 R2 ][GaCl4 ] and [CpAr M(µ-Br)]2 (M=Co and Ni) as well as by using low-valent "CpAr MI " sources. Anion metathesis of 2-R[GaCl4 ] and 3-R[GaCl4 ] was achieved with Na[BArF24 ]. The P5 framework of the resulting salts 2-R[BArF24 ] can be further functionalized with nucleophiles. Thus reactions with [Et4 N]X (X=CN and Cl) give unprecedented cyano- and chloro-functionalized complexes, while organo-functionalization was achieved with CyMgCl.

Construction of alkyl-substituted pentaphosphido ligands in the coordination sphere of cobalt.

Rare mono- and diorganopentaphosphido cobalt complexes are accessible by P-P condensation using the unprecedented, reactive cobalt-gallium tetraphosphido complex [K(dme)2{(MesBIAN)Co(µ-η4:η2-P4)Ga(nacnac)}] (2). Compound 2 was prepared in good yield by reaction of [K(Et2O){(MesBIAN)Co(η4-1,5-cod)}] [1, BIAN = bis(mesitylimino)acenaphthene diimine, cod = 1,5-cyclooctadiene] with [Ga(nacnac)(η2-P4)] (nacnac = CH[CMeN(2,6-iPr2C6H3)]2). Reactions with R2PCl (R = iPr, tBu, and Cy) selectively afford [(MesBIAN)Co(cyclo-P5R2)] (3a-c), which feature η4-coordinated 1,1-diorganopentaphosphido ligands. The mechanism of formation of these species has been studied by 31P{1H} NMR spectroscopy and DFT calculations. In the case of 3a (R = iPr), it was possible to identify the intermediate [(MesBIAN)Co(µ-η4:η2-P5iPr2)Ga(nacnac)] (4) by single-crystal X-ray diffraction. A related, monosubstituted organopentaphosphido cobalt complex [(MesBIAN)Co(µ-η4:η1-P5 tBu)GaCl(nacnac)] (5) was isolated by reacting dichloroalkylphosphane tBuPCl2 with 2. Heterobimetallic complexes such as 2 thus may enable the targeted construction of a range of new metal-coordinated polyphosphorus frameworks by P-P condensation.