Reversible P–C Coupling Reactions at the Unsaturated Dimolybdenum Carbyne Complex [Mo₂(η⁵-C₅H₅)₂(CPh)(μ-PCy₂)(μ-SPh)(CO)]⁺

Abstract

The title complex was formed instantaneously by reacting [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)] with [FeCp2]BF4 in the presence of diphenyl disulfide, but it could not be isolated as a pure material. It most likely displays bridging phosphide and thiolate ligands and essentially terminal carbonyl (Mo–C = 1.987 Å) and carbyne (Mo–C = 1.820 Å) ligands, according to density functional theory calculations. In solution this complex released CO spontaneously to yield the 30-electron complex [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-SPh)]BF4 (Mo–Mo = 2.4772(6) Å), and attempts to crystallize it at low temperature yielded instead the electron-precise aquo derivative [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-SPh)(CO)(OH2)]BF4 (Mo–Mo = 2.7820(4) Å). The addition of CO induced the coupling between the carbyne and phosphide ligands, to yield the tricarbonyl phosphinocarbene complex [Mo2Cp2(μ-η1:η1,κ1-CPhPCy2)(μ-SPh)(CO)3]BF4 (Mo–Mo = 2.928(1) Å). This coupling process was reversible, since the latter complex could be decarbonylated stepwise by thermal methods, to give first the 32-electron phosphinocarbene derivative [Mo2Cp2(μ-η1:η1,κ1-CPhPCy2)(μ-SPh)(CO)2]BF4 (Mo–Mo = 2.7863(4) Å) and eventually yielding [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-SPh)]BF4 via the title complex. In contrast to this behavior, the reaction of the title complex with CN t Bu did not induce a P–C coupling process, but eventually led to the displacement of the thiolate ligand to give the dication trans-[Mo2Cp2(μ-CPh)(μ-PCy2)(CN t Bu)4]2+ via the bis(isocyanide) complex cis-[Mo2Cp2(μ-CPh)(μ-PCy2)(μ-SPh)(CN t Bu)2]BF4, with these differences being probably steric in origin.

Acceptor Behavior and E–H Bond Activation Processes of the Unsaturated Heterometallic Anion [MoReCp(μ-PCy2)(CO)5]−(Mo═Re)

“…2.42 Å. 20 Spectroscopic data in solution for compound 6 are consistent with the geometry found in the crystal. Its IR spectrum displays five C−O stretches, with the three most energetic ones (mainly derived from the Re fragment) displaying the pattern characteristic of pyramidal M(CO) 3 oscillators, 10 while the carbonyl 13 C NMR resonances display the expected P−C couplings, with values for carbonyls trans to the P ligand being larger than those of carbonyls cis to it at the Re fragment, while the opposite holds for the Mo fragment.…”

“…For comparison, the Mo–S distances in the symmetrically bridged cation [Mo 2 Cp 2 (μ-CPh)­(μ-PCy 2 )­(μ-SPh)] + are ca. 2.42 Å …”

C–P vs C–H Bond Cleavage of Triphenylphosphine at Platinum(0): Mechanism of Formation, Reactivity, Redox Chemistry, and NMR Chemical Shift Calculations of a μ-Phosphanido Diplatinum(II) Platform

“…Oxidative P–C bond scission has been recognized as a mechanism for the deactivation of catalytically competent low-coordinate and -valent transition-metal species stabilized by tertiary phosphines. ,− More recently, the inverse process, namely the formation of catalytically competent di- and trinuclear structures of Pd, has been observed to involve C–P bond activation . A chemical stimulus is prerequisite to reverse C–P bond splitting, which includes the dissociation or binding of a spectator ligand − or a metal centered two-electron redox process. − As exemplified in Scheme , initial oxidation by iodine triggers reductive C–P bond reformation from a triangular structure of platinum. , Most notably, P–C­(aryl) bond addition to a low-valent palladium precatalyst has been developed into a catalytic metathesis protocol that allows for exchanging aryl groups at tertiary phosphines …”

Reactions of the Carbyne-Bridged Radical Complex [Mo2(η5-C5H5)2(μ-CPh)(μ-PCy2)(μ-CO)]+ with Bidentate Ligands Having E–H Bonds (E = O, S, N)

“…Remarkably, compound 1 can undergo redox-induced related P–C couplings. Thus, 1 reacts instantaneously with the secondary phosphine HPEt 2 in the presence of [FeCp 2 ]BF 4 , to give the phosphinocarbene derivative [Mo 2 Cp 2 (μ-η 1 :η 1 ,κ 1 -CPhPEt 2 )­(μ-PEt 2 )(CO)­(PHEt 2 )]BF 4 , while its reaction with diphenyl disulfide or HSPh in the presence of [FeCp 2 ]BF 4 gives the thiolate derivative [Mo 2 Cp 2 (μ-SPh)­(μ-PCy 2 )(CO)­(CPh)]BF 4 , a 32-electron complex undergoing a reversible P–C coupling upon carbonylation . These reactions are themselves of interest since only a few examples have been reported of coupling at di- or polynuclear complexes between PR 2 and CR ligands, , even if these P–C couplings are well documented at mononuclear complexes…”