The reactivity of terminal chloroaminophosphido ligands towards metal carbonyl complexes. Formation of μ2- and μ3-phosphinidene clusters

A metal and a metalloid Lewis acid bridged by a μ2-phosphinidene

Dinuclear phosphinidene complexes bridging two transition metal centres are now well established. However, a phosphinidene bridging a metal centre and a main group Lewis acid has not yet been reported. Herein, we describe the generation of a highly reactive phosphinidene complex bridging a tungsten and a boron centre. Furthermore, the synthesis and dyotropic rearrangement of a P-borane adduct of an N-methylimidazole-stabilized neutral, electrophilic terminal phosphinidene complex is reported.

Efficient Synthesis and Multisite Reactivity of a Phosphinidene-Bridged Mo-Re Complex. A Platform Combining Nucleophilic and Electrophilic Features

The heterometallic complex [MoReCp(μ-PR*)(CO)₆] (3) was prepared in 60% overall yield from syn-[MoCp(PHR*)(CO)₂] via a three-step procedure involving complexes syn-[MoCp(PClR*)(CO)₂] and [MoReCp(μ-PR*)(CO)₇] as intermediate species (R* = 2,4,6-C₆H₂^tBu₃). The PR* ligand in 3 displays a novel asymmetric interaction with the dimetal center, involving a double bond with one atom (Mo) and a dative single bond with the other one (Re). Compound 3 underwent thermal isomerization involving a C-H bond cleavage to yield the hydride [MoReCp(μ-H){μ-P(CH₂CMe₂)C₆H₂^tBu₂}(CO)₆] and reacted with I₂ to give [MoReCpI₂(μ-PR*)(CO)₆], which displays a symmetrical phosphinidene bridge. Its reaction with methyl propiolate at 293 K proceeded with [2 + 2] cycloaddition of the alkyne and decarbonylation to yield the phosphapropenylidene-bridged complex [MoReCp{μ-κ²_P,C:η³-PR*CHC(CO₂Me)}(CO)₅] as the major product, whereas its reaction with excess CN(4-C₆H₄OMe) at 273 K proceeded with formal [2 + 1] cycloaddition of the isocyanide and further isocyanide addition at the Re site to yield the complex [MoReCp{μ-η²_P,C:κ¹_P-PR*CN(4-C₆H₄OMe)}(CO)₆{CN(4-C₆H₄OMe)}], which displays an azaphosphaallene ligand in a novel bridging coordination mode.

One-step synthesis and P-H bond cleavage reactions of the phosphanyl complex syn-[MoCp{PH(2,4,6-C6H2tBu3)}(CO)2] to give heterometallic phosphinidene-bridged derivatives

Photolysis of [Mo2Cp2(CO)6] and PH2R* (R* = 2,4,6-C6H2tBu3) yielded the title complex, which turned out to be a versatile precursor of novel heterometallic phosphinidene-bridged complexes via three different P-H bond activation processes: photolysis, deprotonation and reduction. In this way the new complexes [MoReCp(μ-PR*)(CO)n] (n = 6,7), [MoFeCp2(μ-PR*)(CO)m], (m = 3, 4) and [MoAuCp(μ-PR*)(CO)2{P(p-tol)3}] were prepared.

Phosphinidene-Bridged MoMn Derivatives of the Thiophosphinidene Complex [Mo2Cp2(μ-κ2:κ1,η6-SPMes*)(CO)2] (Mes* = 2,4,6-C6H2tBu3)

The title complex (1) reacted with [Mn₂(CO)₁₀] under visible-UV irradiation (toluene solution and quartz glassware) to give a mixture of the phosphinidene complex [MnMoCp(μ-κ¹:κ¹,η⁶-PMes*)(CO)₄], the cluster [Mn₂Mo₂Cp₂(μ-κ¹:κ¹,η⁶-PMes*)(μ₃-S)(CO)₈], and the thiophosphinidene complex [MnMoCp(μ-κ²:κ¹,η⁴-SPMes*)(CO)₅], in yields of ca. 60, 20, and 10% respectively (Mes* = 2,4,6-C₆H₂^tBu₃). The major product follows from formal replacement of the SMoCp(CO)₂ fragment in 1 with a Mn(CO)₄ fragment, and displayed multiple bonding to phosphorus (Mn-P = 2.1414(8) Å); the tetranuclear cluster results from formal insertion of a Mn₂(CO)₆ fragment in 1, with cleavage of P-S and P-Mo bonds, to render a μ₃-S bridged Mn₂Mo core bearing an exocyclic phosphinidene ligand involved in multiple bonding to one of the Mn atoms (Mn-P = 2.140(2) Å); the thiophosphinidene complex (Mn-P = 2.294(1) Å) formally results from addition of sulfur and carbon monoxide to the major MnMo product, a transformation which actually could be performed stepwise, via the MnMo thiophosphinidene complex [MnMoCp(μ-κ²:κ¹,η⁶-SPMes*)(CO)₄]. When the photolysis of 1 and [Mn₂(CO)₁₀] was performed in tetrahydrofuran solution and using conventional glassware, then the V-shaped cluster [Mn₂MoCp{μ-κ¹:κ¹:κ¹,η⁵-P(C₆H₃^tBu₃)}(CO)₈] was obtained selectively (Mo-Mn = 3.2910(5) Å, Mn-Mn = 2.9223(5) Å), which unexpectedly displays a cyclohexadienylidene-phosphinidene ligand resulting from H atom abstraction at the aryl ring of the precursor. Density functional theory calculations on the complexes [L_nM(μ-κ¹:κ¹,η⁶-PMes*)MoCp] (ML_n = MoCp(CO)₂, Mn(CO)₄, Co(CO)₃) revealed that the degree of delocalization of the metal-phosphorus π-bonding interaction over the Mo-P-M chain is significantly conditioned by the heterometal fragment ML_n, it being increased in the order Mn ≤ Mo < Co.

Insight into the Reaction of a Dinuclear Phosphinidene Complex with Nitriles

The phosphinidene complex [Cp*P{W(CO)5}2] (1; Cp*=C5 Me5 ) reacted with malononitrile to give the 1,2-dihydro-1,3,2-diazaphosphinine derivative 2. The reaction of 1 with 1,4-benzodinitrile gave [1,4-{{W(CO)5}2 P-N=C(Cp*)}2 (C6 H4)] (3), the first example of a cumulene-like aminophosphinidene complex. The reaction of 1 with aniline gave the aminophosphinidene complex [(Ph)N(H)P{W(CO)5}2] (4). To compare the reactivity of benzonitrile and aniline with 1, the phosphinidene complex 1 was reacted with three different isomers of aminobenzonitrile (2-, 3-, and 4-aminobenzonitrile). These reactions gave an insight into the reaction pathway of 1 with benzonitrile derivatives. Compounds 5, 6 a, 6 b, and 7, which are derivatives of 1,2-dihydro-1,3,2-diazaphosphinine or benzo-2H-1,2-azaphospholes, were, as well as all other products, characterized by mass spectrometry, NMR and IR spectroscopy, and X-ray structure analysis.

P-S bond cleavage in reactions of thiophosphinidene-bridged dimolybdenum complexes with [Co2(CO)8] to give phosphinidene-bridged heterometallic derivatives

The thiophosphinidene complex [Mo2Cp2(μ-κ(2):κ(1),η(6)-SPMes*)(CO)2] (Mes* = 2,4,6-C6H2(t)Bu3) reacted with [Co2(CO)8] at room temperature or below to give several of the following phosphinidene-bridged products, depending on reaction conditions: the MoCo complexes [CoMoCp(μ-κ(1):κ(1),η(6)-PMes*)(CO)3] and [CoMoCp(μ-PMes*)(CO)5] (Co-Mo = 2.972(1) Å), the MoCo3 cluster [Co3MoCp(μ3-PMes*)(CO)9] (Co-Mo = 2.664(1), 2.810(1) Å), and the sulphido-bridged tetranuclear complexes [Co2Mo2Cp2(μ-κ(1):κ(1):κ(1),η(4)-PMes*)(μ3-S)(CO)7] and [Co3MoCp(μ-κ(1):κ(1):κ(1),η(4)-PMes*)(μ3-S)(CO)8]. In contrast, the thiophosphinidene complex [Mo2Cp2(μ-κ(2):κ(1),η(4)-SPMes*)(CO)3] reacted with the same cobalt reagent selectively to give the above Mo2Co2 complex in very high yield. The latter could be decarbonylated photochemically to give [Co2Mo2Cp2(μ-κ(1):κ(1):κ(1),η(6)-PMes*)(μ3-S)(CO)6] (Co-Co = 2.435(3), Co-Mo = 2.769(2), 2.798(2) Å), after an η(4)- to η(6)-haptotropic rearrangement of the aryl ring of the phosphinidene ligand that could be reversed upon reaction with CO. The related complex [Mo2Cp2(μ-κ(2):κ(1),η(4)-SPMes*)(CO)2(CN(t)Bu)], however, displayed poor selectivity towards the cobalt dimer and yielded a mixture of CoMo complexes [CoMoCp(μ-PMes*)(CO)5] and [CoMoCp(μ-PMes*)(CO)3(CN(t)Bu)2], and the tetranuclear sulphido-bridged ones [Co2Mo2Cp2(μ-κ(1):κ(1):κ(1),η(4)-PMes*)(μ3-S)(CO)6(CN(t)Bu)] (Co-Co = 2.533(1), Co-Mo = 2.7485(9), 2.770(1) Å) and [Co3MoCp(μ-κ(1):κ(1):κ(1),η(4)-PMes*)(μ3-S)(CO)7(CN(t)Bu)] (Co-Co = 2.4120(7) to 2.5817(7) Å). This reduction in selectivity might have an electronic origin rather than a steric origin, since the related but cationic substrate [Mo2Cp2{μ-κ(2):κ(1),η(5)-SP(C6H3(t)Bu3)}(CO)2(CN(t)Bu)]BAr [Ar' = 3,5-C6H3(CF3)2] reacted with [Co2(CO)8] more selectively to give the sulphido-bridged Co2Mo2 complex [Co2Mo2Cp2{μ-κ(1):κ(1):κ(1),η(5)-P(C6H3(t)Bu3)}(μ3-S)(CO)6(CN(t)Bu)]BAr, along with small amounts of the Co3Mo complex [Co3MoCp{μ-κ(1):κ(1):κ(1),η(5)-P(C6H3(t)Bu3)}(μ3-S)(CO)7(CN(t)Bu)]BAr (Co-Co = 2.414(2) to 2.560(2) Å). The structure of the new complexes was analyzed on the basis of the corresponding X-ray diffraction and spectroscopic data, and likely reaction pathways were discussed on the basis of the above results and some additional experiments.

The formation of mixed metal aminophosphinidene clusters via reactions of terminal chloroaminophosphido complexes with Co2(CO)8

Reactions of terminal chloroaminophosphido complexes with Co2(CO)8 have been examined. The ruthenium phosphido complexes [Cp*Ru(CO)2{P(Cl)TMP}] (1a) and [CpRu(CO)2{P(Cl)TMP}] (1b) (TMP = 2,2,6,6-tetramethylpiperidinyl) react with Co2(CO)8 to form the cobalt cluster [Co4(CO)7(µ-CO)3{µ3-P(TMP)}] (2) with complete transfer of the phosphinidene unit to cobalt. In contrast, the phosphido complex [Cp*Ru(CO)2{P(Cl)N-i-Pr2}] (1c) affords the spiked-triangular cluster [Cp*RuCo3(CO)8(µ-CO)2(µ3-PN-i-Pr2)] (3), which retains the Cp*Ru unit upon reaction with Co2(CO)8. The molybdenum phosphido complex [CpMo(CO)2{P(Cl)TMP}] (4) reacts with Co2(CO)8 to form cluster 2, while [Cp*Mo(CO)3{P(Cl)N-i-Pr2}] (5) generates the mixed metal tetrahedral cluster [Cp*MoCo3(CO)5(µ-CO)4(µ3-PN-i-Pr2)] (6). Key words: phosphido, phosphinidene, cobalt, ruthenium, molybdenum, cluster.