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

Abstract

The thiophosphinidene complex [Mo₂Cp₂(μ–κ²:κ¹,η⁶-SPMes*)(CO)₂] (Mes* = 2,4,6-C₆H₂^tBu₃) 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–κ¹:κ¹,η⁶-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–κ¹:κ¹:κ¹,η⁴-PMes*)(μ₃-S)(CO)₇] and [Co₃MoCp(μ–κ¹:κ¹:κ¹,η⁴-PMes*)(μ₃-S)(CO)₈]. In contrast, the thiophosphinidene complex [Mo₂Cp₂(μ–κ²:κ¹,η⁴-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–κ¹:κ¹:κ¹,η⁶-PMes*)(μ₃-S)(CO)₆] (Co–Co = 2.435(3), Co–Mo = 2.769(2), 2.798(2) Å), after an η⁴- to η⁶-haptotropic rearrangement of the aryl ring of the phosphinidene ligand that could be reversed upon reaction with CO. The related complex [Mo₂Cp₂(μ–κ²:κ¹,η⁴-SPMes*)(CO)₂(CN^tBu)], 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^tBu)₂], and the tetranuclear sulphido-bridged ones [Co₂Mo₂Cp₂(μ–κ¹:κ¹:κ¹,η⁴-PMes*)(μ₃-S)(CO)₆(CN^tBu)] (Co–Co = 2.533(1), Co–Mo = 2.7485(9), 2.770(1) Å) and [Co₃MoCp(μ–κ¹:κ¹:κ¹,η⁴-PMes*)(μ₃-S)(CO)₇(CN^tBu)] (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–κ²:κ¹,η⁵-SP(C₆H₃^tBu₃)}(CO)₂(CN^tBu)]BAr^′₄ [Ar′ = 3,5-C₆H₃(CF₃)₂] reacted with [Co₂(CO)₈] more selectively to give the sulphido-bridged Co₂Mo₂ complex [Co₂Mo₂Cp₂{μ–κ¹:κ¹:κ¹,η⁵-P(C₆H₃^tBu₃)}(μ₃-S)(CO)₆(CN^tBu)]BAr^′₄, along with small amounts of the Co₃Mo complex [Co₃MoCp{μ–κ¹:κ¹:κ¹,η⁵-P(C₆H₃^tBu₃)}(μ₃-S)(CO)₇(CN^tBu)]BAr^′₄ (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.