Dimolybdenum Cyclopentadienyl Complexes with Bridging Chalcogenophosphinidene Ligands

The reactions of the phosphinidene-bridged complex [Mo2Cp2(μ-PH)­(η6-HMes*)­(CO)2] (1), the arylphosphinidene complexes [Mo2Cp2(μ-κ1:κ1,η6-PMes*)­(CO)2] (2), [Mo2Cp2(μ-κ1:κ1,η4-PMes*)­(CO)3] (3), [Mo2Cp2(μ-κ1:κ1,η4-PMes*)­(CO)2(CNtBu)]
(4), and the cyclopentadienylidene-phosphinidene complex
[Mo2Cp­(μ-κ1:κ1,η5-PC5H4)­(η6-HMes*)­(CO)2] (5) toward different sources of chalcogen atoms
were investigated (Mes* = 2,4,6-C6H2tBu3; Cp = η5-C5H5). 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 [Mo2Cp2{μ-κ2P,Z:κ1P-ZPH}­(η6-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
[Mo2Cp2(μ-κ2P,Z:κ1P,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-κ2P,S:κ1S′,η6-S2PMes*)­(CO)2], in the reaction with
sulfur. The η4-complexes 3 and 4 reacted with sulfur and gray selenium to give the corresponding
derivatives [Mo2Cp2(μ-κ2P,Z:κ1P,η4-ZPMes*)­(CO)2L] (L = CO, CNtBu), 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 5 reacted
with all chalcogens, and gave with good yields the chalcogenophosphinidene
derivatives [Mo2Cp­(μ-κ2P,Z:κ1P,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-κ2P,S:κ1S′,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 syn-[Mo2Cp2(μ-κ2P,S:κ1P,η4-SPMes*)­(CO)3].