The title phosphinidene complex reacted at room temperature with CS 2 and SCNPh to give the phosphanyl derivatives [Mo 2 Cp{- 2

The title phosphinidene complex could be sequentially protonated with HBF4·OEt2 or [H(OEt2)2](BAr'4) to give the phosphido-bridged derivatives [Mo2Cp(μ-κ(1):κ(1),η(5)-HPC5H4)(η(6)-HMes*)(CO)2(PMe3)]X and then the hydrides [Mo2Cp(H)(μ-κ(1):κ(1),η(5)-HPC5H4)(η(6)-HMes*)(CO)2(PMe3)]X2 (X = BF4, BAr'4; Ar' = 3,5-C6H3(CF3)2; Mes* = 2,4,6-C6H2(t)Bu3). Density functional theory (DFT) calculations revealed that the most favored site for initial electrophilic attack is the metallocene Mo atom, but attachment of the electrophile to the phosphinidene P atom gives more stable products. This was in agreement with all other reactions investigated, which invariably involved the attachment of the added electrophile at the P site. Thus, the title compound reacted with S8 at 223 K to give the thiophosphinidene-bridged complex [Mo2Cp{μ-κ(1):κ(1),η(5)-P(S)C5H4}(η(6)-HMes*)(CO)2(PMe3)], a poorly stable molecule which reacted with MeI at room temperature to give the corresponding thiolatophosphido derivative, isolated as [Mo2Cp{μ-κ(1):κ(1),η(5)-P(SMe)C5H4}(η(6)-HMes*)(CO)2(PMe3)](BAr'4) (P-S = 2.128(4) Å) after anion exchange with Na(BAr'4). Reaction of the title compound with MeI proceeded smoothly to give the corresponding methylphosphido derivative, isolated analogously as [Mo2Cp{μ-κ(1):κ(1),η(5)-P(Me)C5H4}(η(6)-HMes*)(CO)2(PMe3)](BAr'4). The related complex [Mo2Cp{μ-κ(1):κ(1),η(5)-P(Me)C5H4}(η(6)-HMes*)(CO)2(PMe2Ph)](BAr'4) (P-C(Me) = 1.841(5) Å) could be prepared analogously from the neutral precursor [Mo2Cp{μ-κ(1):κ(1),η(5)-PC5H4}(η(6)-HMes*)(CO)2(PMe2Ph)]. In contrast, reaction of the title complex with ethylene sulfide involved opening of the C2S ring and formation of new P-C and Mo-S bonds (1.886(7) and 2.493(2) Å, respectively), with displacement of the PMe3 ligand, to give the phosphido-thiolato complex [Mo2Cp{μ-κ(2)(P,S):κ(1)P,η(5)-P(C2H4S)C5H4}(η(6)-HMes*)(CO)2]. All these derivatives of the title complex displayed an unusual trigonal pyramidal-like environment around the bridging P atom, with the added electrophile placed in the Mo2P plane as a result of the directionality of the relevant frontier orbital of the phosphinidene complex, according to DFT calculations.

A novel dimerization of maleic anhydride involving olefinic to carbonyl C−C coupling and an [1,7]-H shift is promoted by a strongly nucleophilic pyramidal phosphinidene complex. The resulting carbene is stabilized by coordination of the P atom of the phosphinidene ligand and undergoes keto/enol tautomerization when going from solution to the solid state. This is accompanied by a strong pyramidalization of the ylidic carbon atom, facilitated by the presence of π•••π stacking interactions in the crystal lattice.

The title complex reacted readily with CS 2 and SCNPh to give the phosphinidenecumulene adducts [Mo 2 Cp{-

The reactivity of complex [Mo2Cp(- 1 : 1 , 5 -PC5H4)(CO)2( 6 -HMes*)(PMe3)] (1) toward different diazoalkanes and organic azides was investigated. The pyramidal phosphinidene ligand in 1 displayed a strong nucleophilicity enabling these reactions to proceed rapidly even below room temperature. Thus, 1 reacted rapidly at 253 K with different diazoalkanes N2CRR' (RR' = HH, PhPh, HCO2Et) to give the corresponding P:P-bridged phosphadiazadiene derivatives as major products which, however, could not be isolated. Reaction of the latter with [H(OEt2)2](BAr'4) yielded the corresponding cationic derivatives [Mo2Cp{- 1 P: 1 P, 5 -P(NHNCRR')C5H4}( 6 -HMes*)(CO)2(PMe3)](BAr'4), which were isolated in ca. 70% yield. A related species [Mo2Cp{- 1 P: 1 P, 5 -P(NMeNCHCO2Et)C5H4}( 6 -HMes*)(CO)2(PMe3)](BAr'4) was isolated upon reaction of the ethyl diazoacetate derivative with MeI and subsequent anion exchange with Na(BAr'4). Reaction of 1 with aryl azides (4-C6H4Me)N3 and (4-C6H4F)N3 proceeded rapidly at low temperature to give possibly the corresponding P:Pbridged phosphaimine derivatives as major products, which could be neither isolated. Protonation of these products with [H(OEt2)2](BAr'4) gave the corresponding aminophosphanyl complexes [Mo2Cp{- 1 P: 1 P, 5 -P(NHR)C5H4}( 6 -HMes*)(CO)2(PMe3)](BAr'4), isolated in ca. 75% yield. In contrast, the result of reactions of 1 with benzyl azide was strongly dependent on temperature, including the temperature in the subsequent methylation step that gave isolable cationic derivatives. By careful choice of experimental conditions, different complexes having methylated phosphatriazadiene ligands were isolated, such as [Mo2Cp{- 1 P: 1 P, 5 -P(NNNMeCH2Ph)C5H4}( 6 -HMes*)(CO)2(PMe3)](BAr'4), and the metallacyclic derivatives syn-and anti-[Mo2Cp{- 2 P,N: 1 P, 5 -P(NMeNNCH2Ph)C5H4}( 6 -HMes*)(CO)(PMe3)](BAr'4). Density functional theory calculations, along with NMR monitoring experiments, revealed that the formation of the latter products stemmed from different and kinetically favored phosphatriazadiene intermediates,