The reactions of the phosphinidene-bridged complex [Mo(2)Cp(2)(μ-PH)(η(6)-HMes*)(CO)(2)] (1), the arylphosphinidene complexes [Mo(2)Cp(2)(μ-κ(1):κ(1),η(6)-PMes*)(CO)(2)] (2), [Mo(2)Cp(2)(μ-κ(1):κ(1),η(4)-PMes*)(CO)(3)] (3), [Mo(2)Cp(2)(μ-κ(1):κ(1),η(4)-PMes*)(CO)(2)(CN(t)Bu)] (4), and the cyclopentadienylidene-phosphinidene complex [Mo(2)Cp(μ-κ(1):κ(1),η(5)-PC(5)H(4))(η(6)-HMes*)(CO)(2)] (5) toward different sources of chalcogen atoms were investigated (Mes* = 2,4,6-C(6)H(2)(t)Bu(3); Cp = η(5)-C(5)H(5)). The bare elements were appropriate sources in all cases except for oxygen, in which case dimethyldioxirane gave the best results. Complex 1 reacted with the mentioned chalcogen sources at low temperature, to give the corresponding chalcogenophosphinidene derivatives [Mo(2)Cp(2){μ-κ(2)(P,Z):κ(1)(P)-ZPH}(η(6)-HMes*)(CO)(2)] (Z = O, S, Se, Te; P-Se = 2.199(2) Å). The arylphosphinidene complex 2 was the least reactive substrate and gave only chalcogenophosphinidene derivatives [Mo(2)Cp(2)(μ-κ(2)(P,Z):κ(1)(P),η(6)-ZPMes*)(CO)(2)] for Z = O and S (P-O = 1.565(2) Å), along with small amounts of the dithiophosphorane complex [Mo(2)Cp(2)(μ-κ(2)(P,S):κ(1)(S'),η(6)-S(2)PMes*)(CO)(2)], in the reaction with sulfur. The η(4)-complexes 3 and 4 reacted with sulfur and gray selenium to give the corresponding derivatives [Mo(2)Cp(2)(μ-κ(2)(P,Z):κ(1)(P),η(4)-ZPMes*)(CO)(2)L] (L = CO, CN(t)Bu), obtained respectively as syn (Z = Se; P-Se = 2.190(1) Å for L = CO) or a mixture of syn and anti isomers (Z = S; P-S = 2.034(1)-2.043(1) Å), with these diastereoisomers differing in the relative positioning of the chalcogen atom and the terminal ligand at the metallocene fragment, relative to the Mo(2)P plane. The cyclopentadienylidene compound 5 reacted with all chalcogens, and gave with good yields the chalcogenophosphinidene derivatives [Mo(2)Cp(μ-κ(2)(P,Z):κ(1)(P),η(5)-ZPC(5)H(4))(η(6)-HMes*)(CO)(2)] (Z = S, Se, Te), these displaying in solution equilibrium mixtures of the corresponding cis and trans isomers differing in the relative positioning of the cyclopentadienylic rings with respect to the MoPZ plane in each case. The sulfur derivative reacted with excess sulfur to give the dithiophosphorane complex [Mo(2)Cp(μ-κ(2)(P,S):κ(1)(S'),η(5)-S(2)PC(5)H(4))(η(6)-HMes*)(CO)(2)] (P-S = 2.023(4) and 2.027(4) Å). The structural and spectroscopic data for all chalcogenophosphinidene complexes suggested the presence of a significant π(P-Z) bonding interaction within the corresponding MoPZ rings, also supported by Density Functional Theory calculations on the thiophosphinidene complex syn-[Mo(2)Cp(2)(μ-κ(2)(P,S):κ(1)(P),η(4)-SPMes*)(CO)(3)].

A method for the generation of transition metal-phosphorus multiple bonds has been developed using the reactions of a novel thiophosphinidene-bridged dimolybdenum complex with different metal carbonyls. The overall process could be considered as a transmetalation of the phosphinidene ligand involving the activation of P-S and P-Mo bonds.

The sequential addition of H⁺ and H⁻ ions to [Mo₂Cp₂(μ-κ²P,S:κ¹P,η⁴-SPMes*)(CNtBu)(CO)₂] (Mes* = 2,4,6-C₆H₂tBu₃) completes a hydrocarbation or hydronitration of the uncoordinated C=C bond of the Mes* ring, yielding new ligands with thiophosphinidene and aldimine or aminocarbene functions tethered to a η⁴-cyclohexadiene ring. The H⁻ ion first attacks a Cp group to give a cyclopentadiene complex which evolves via a hydride intermediate.

Reactions of the chalcogenophosphinidene‐bridged complexes syn‐[Mo2Cp2(μ‐κ2P,Z:κ1P,η4‐ZPMes*)(CO)2L] (L = CO, CNtBu; Z = O, S, Se), anti‐[Mo2Cp2(μ‐κ2P,S:κ1P,η4‐SPMes*)(CO)2L] (L = CO, CNtBu) and [Mo2Cp2{μ‐κ2P,Z:κ1P‐ZPH}(η6‐HMes*)(CO)2] (Z = S, Se, Te) towards sources of H+, Me+, and AuP(pTol)3+ cations were investigated (Mes* = 2,4,6‐C6H2tBu3; Cp = η5‐C5H5). The latter two electrophiles invariably added to the chalcogen atom to give corresponding derivatives [Mo2Cp2{μ‐κ2P,Z:κ1P,η4‐Mes*PZ(CH3)}(CO)3]BX4 [X = F, Z = O, S, Se; P–S 2.144(1) Å when Z = S and X = Ar′ = 3,5‐C6H3(CF3)2], [Mo2Cp2{μ‐κ2P,Z:κ1P,η4‐Mes*PZ(CH3)}(CNtBu)(CO)2]BF4 (Z = S, Se), and [AuMo2Cp2(μ3‐κ1S:κ2P,S:κ1P,η4‐SPMes*){P(pTol)3}(CO)3]PF6 [P–S 2.113(2), S–Au 2.320(2) Å]. Even when syn and anti isomers of the neutral precursor were used, the corresponding products were invariably characterized by their syn conformation (Z atom close to L ligand). Besides this, methylated derivatives of the chalcogenophosphinidene complexes bearing the formula [Mo2Cp2{μ‐κ2P,Z:κ1P‐HPZ(Me)}(η6‐HMes*)(CO)2](CF3SO3) (Z = S, Se, Te), were found in solution to exist as an equilibrium of corresponding cis and trans isomers differing, in each case, in the relative positioning of the Cp rings with respect to the MoPZ plane. In contrast to the above results, the protonation of all these compounds was quite sensitive to the particular chalcogenophosphinidene ligand and conformation of the complex. Protonation of the HPZ‐bridged complexes led to complex mixtures of products that could not be isolated or properly characterized. In contrast, the aryl‐bearing substrates reacted selectively to give corresponding complexes [Mo2Cp2{μ‐κ2P,Z:κ1P,η5‐ZP(C6H3tBu3)}(CO)3]BX4 (Z = S, X = F; P–S 2.032(2) Å when X = Ar′; Z = Se, X = F) and [Mo2Cp2{μ‐κ2P,Z:κ1P,η5‐ZP(C6H3tBu3)}(CNtBu)(CO)2]BAr′4 (Z = S, Se). The reaction of anti‐[Mo2Cp2(μ‐κ2P,S:κ1P,η4‐SPMes*)(CO)3] with HBF4·OEt2 at 213 K initially gave unstable intermediate anti‐[Mo2Cp2{μ‐κ2P,S:κ1P,η4‐Mes*PS(H)}(CO)3]BF4, which then rapidly converted at room temperature to the conventional isomer with the S atom close to the metallocene‐bound carbonyl ligand (syn isomer). This transformation is in agreement with Density Functional Theory calculations for neutral thiophosphinidene complexes; electrophilic attack at the sulfur atom, which is both an orbital‐ and charge‐favoured event, affords products that are more stable than those resulting from protonation at the metal sites. All these protonation reactions eventually result in an endo addition of H+ to the C6 atom of the Mes* ring with concomitant η4→η5 haptotropic shift of the resulting HMes* group. This conversion involves an easy H migration from S to the C6 atom, computed to take place with a low activation barrier of about 70 kJ/mol.

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.

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Reaction of [Mo Cp (μ-κ :κ ,η -PMes*)(CO) ] with S or Se followed by protonation with [H(OEt ) ](BAr' ) gave the cationic derivatives [Mo Cp {μ-κ :κ ,η -EP(C H tBu )}(CNR)(CO) ](BAr' ) (E=S; R=tBu, iPr, Ph, 4-C H OMe, Xyl; or E=Se; R=tBu; Ar'=3,5-C H (CF ) ). Reaction of the latter with K[BHsBu ] yielded the aldimine complexes [Mo Cp {μ-κ :κ ,η -SP(C H tBu (CHNR))}(CO) ] and their aminocarbene isomers [Mo Cp {μ-κ :κ ,η -SP(C H tBu (NRCH))}(CO) ] (R ≠ Xyl), following C-C and C-N couplings, respectively. Monitoring of these reactions revealed that the initial H attack takes place at a Cp ligand to give cyclopentadiene intermediates [Mo Cp{μ-κ :κ ,η -SP(C H tBu )}(η -C H )(CNR)(CO) ], which then undergo C-H oxidative addition to give the hydride isomers [Mo Cp {μ-κ :κ ,η -SP(C H tBu )}(H)(CNR)(CO) ]. In turn, the latter rearrange to give the aldimine and aminocarbene complexes. DFT calculations revealed that the hydride intermediates first undergo migratory insertion of the isocyanide ligand into the Mo-H bond to give unobservable formimidoyl intermediates, which then evolve either by nucleophilic attack of the N atom on the C ring (C-N coupling) or by migratory insertion of the formimidoyl ligand into the C ring (C-C coupling). Our data suggest that increasing the size of the substituent R at the isocyanide ligand destabilizes the aldimine isomer to a greater extent, thus favoring formation of the aminocarbene complex.

The phosphinidene-bridged complexes [Mo2Cp2(μ-κ(1):κ(1),η(6)-PR*)(CO)2] (1), [Mo2Cp2(μ-κ(1):κ(1),η(4)-PR*)(CO)3] (2), [Mo2Cp(μ-κ(1):κ(1),η(5)-PC5H4)(η(6)-HR*)(CO)2] (3), and [Mo2Cp2(μ-κ(1):κ(1)-PH)(η(6)-HR*)(CO)2] (4) were examined as precursors of heterometallic gold(I) and related derivatives (Cp = η(5)-C5H5, R* = 2,4,6-C6H2(t)Bu3). These complexes reacted with [AuCl(THT)] to give the corresponding derivatives [AuMo2ClCp2(μ-κ(1):κ(1):κ(1),η(6)-PR*)(CO)2], [AuMo2ClCp2(μ-κ(1):κ(1):κ(1),η(4)-PR*)(CO)3] (Au-Mo = 2.8493(6) Å), [AuMo2ClCp(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*)], and [AuMo2ClCp2(μ3-PH)(CO)2(η(6)-HR*)] formally resulting from the addition of an acceptor AuCl moiety to the short Mo-P bond of the parent substrates almost perpendicular to the corresponding Mo2P plane. The chloride ligand was easily displaced upon reaction of the PC5H4-bridged gold complex with K[MoCp(CO)3] to give the tetranuclear derivative [AuMo3Cp2(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)5(η(6)-HR*)] (Au-Mo = 2.711(2) and 2.807(2) Å). Compound 1 also reacted with HgI2 to give a hexanuclear complex [HgMo2Cp2(μ-I)I(μ-κ(1):κ(1),η(6)-PR*)(CO)2]2 containing dative Mo→Hg bonds (2.820(1) and 2.827(1) Å), whereas complex 3 gave the μ3-PR bridged complex [HgMo2CpI2(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*)]. Complexes 1 to 4 also reacted easily with [AuL(THT)]PF6 (L = THT, P(p-tol)3, PMe3, P(i)Pr3) to give the corresponding cationic trinuclear derivatives [AuMo2Cp2(μ-κ(1):κ(1):κ(1),η(6)-PR*)(CO)2L](PF6) (Au-Mo = 2.8080(3) Å for L = P(p-tol)3), [AuMo2Cp2(μ-κ(1):κ(1):κ(1),η(4)-PR*)(CO)3L](PF6), and [AuMo2Cp(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*){P(p-tol)3}](PF6). The blue, analogous PH-bridged complexes were more conveniently isolated as tetra-arylborate salts [AuMo2Cp2(μ3-PH)(CO)2(η(6)-HR*)L](BAr'4) (Au-Mo = 2.8038(6) Å for L = P(i)Pr3; Ar'= 3,5-C6H3(CF3)2]. Compounds 1, 3, and 4 reacted readily with the cation [Au(THT)2](+) (as PF6(-) or BAr'4(-) salts) in a 2:1 ratio to give respectively the corresponding pentanuclear derivatives [Au{Mo2Cp2(μ-κ(1):κ(1):κ(1),η(6)-PR*)(CO)2}2](PF6), [Au{Mo2Cp(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*)}2](PF6) (Au-Mo = 2.7975(7) and 2.8006(7) Å), and [Au{Mo2Cp2(μ3-PH)(CO)2(η(6)-HR*)}2](BAr'4) (Au-Mo = 2.8233(8) and 2.8691(7) Å). Related silver complexes were obtained from the reaction of 3 and 4 with [AgCl(PPh3)]4 after spontaneous symmetrization, while reaction of 1 with [Cu(NCMe)4]PF6 in a 2:1 ratio yielded the analogous copper complex [Cu{Mo2Cp2(μ-κ(1):κ(1):κ(1),η(6)-PR*)(CO)2}2](PF6). All the above cationic gold complexes having (μ-κ(1):κ(1):κ(1),η(6)-PR*) ligands (but not the copper complex) rearranged into [Au{Mo2Cp(μ-κ(1):κ(1):κ(1),η(5)-PC5H4)(CO)2(η(6)-HR*)}2](PF6) in refluxing 1,2-dichloroethane solution.