Dimolybdenum Cyclopentadienyl Complexes with Bridging Chalcogenophosphinidene Ligands

The reactions of the phosphinidene-bridged complex [Mo₂Cp₂(μ-PH)­(η⁶-HMes*)­(CO)₂] (<b>1</b>), the arylphosphinidene complexes [Mo₂Cp₂(μ-κ¹:κ¹,η⁶-PMes*)­(CO)₂] (<b>2</b>), [Mo₂Cp₂(μ-κ¹:κ¹,η⁴-PMes*)­(CO)₃] (<b>3</b>), [Mo₂Cp₂(μ-κ¹:κ¹,η⁴-PMes*)­(CO)₂(CN^<i>t</i>Bu)] (<b>4</b>), and the cyclopentadienylidene-phosphinidene complex [Mo₂Cp­(μ-κ¹:κ¹,η⁵-PC₅H₄)­(η⁶-HMes*)­(CO)₂] (<b>5</b>) toward different sources of chalcogen atoms were investigated (Mes* = 2,4,6-C₆H₂^<i>t</i>Bu₃; Cp = η⁵-C₅H₅). The bare elements were appropriate sources in all cases except for oxygen, in which case dimethyldioxirane gave the best results. Complex <b>1</b> reacted with the mentioned chalcogen sources at low temperature, to give the corresponding chalcogenophosphinidene derivatives [Mo₂Cp₂{μ-κ²_P,Z:κ¹_P-ZPH}­(η⁶-HMes*)­(CO)₂] (Z = O, S, Se, Te; P–Se = 2.199(2) Å). The arylphosphinidene complex <b>2</b> was the least reactive substrate and gave only chalcogenophosphinidene derivatives [Mo₂Cp₂(μ-κ²_P,Z:κ¹_P,η⁶-ZPMes*)­(CO)₂] for Z = O and S (P–O = 1.565(2) Å), along with small amounts of the dithiophosphorane complex [Mo₂Cp₂(μ-κ²_P,S:κ¹_S′,η⁶-S₂PMes*)­(CO)₂], in the reaction with sulfur. The η⁴-complexes <b>3</b> and <b>4</b> reacted with sulfur and gray selenium to give the corresponding derivatives [Mo₂Cp₂(μ-κ²_P,Z:κ¹_P,η⁴-ZPMes*)­(CO)₂L] (L = CO, CN^<i>t</i>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 Mo₂P plane. The cyclopentadienylidene compound <b>5</b> reacted with all chalcogens, and gave with good yields the chalcogenophosphinidene derivatives [Mo₂Cp­(μ-κ²_P,Z:κ¹_P,η⁵-ZPC₅H₄)­(η⁶-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 [Mo₂Cp­(μ-κ²_P,S:κ¹_S′,η⁵-S₂PC₅H₄)­(η⁶-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 <i>syn</i>-[Mo₂Cp₂(μ-κ²_P,S:κ¹_P,η⁴-SPMes*)­(CO)₃]