Complexes from Ring Opening of Lawesson's Reagent and Phosphorus−Phosphorus Coupling

At ambient temperature the reaction of [CpCr(CO)3]2 (1; Cp = η5-C5H5) with 1 mol equiv
of Lawesson's reagent, Ar2P2S4 (2; Ar = C6H4OCH3), for 3 h led to the isolation of brown
crystals of Cp2Cr2(CO)5(SPAr) (3), dark red solids of Cp2Cr2(CO)5(S2PAr) (4), deep blue solids
of Cp2Cr2(S2P(O)Ar)2 (5), greenish yellow solids of CpCr(CO)3H (9), and deep green crystals
of Cp2Cr2(CO)4S (10) with yields of 5, 11, 20, 7, and 8%, respectively; a similar reaction at
90 °C for 2 h gave 5 (36%), CpCr(CO)2(SP(H)Ar) (6) as red crystals (9%), [CpCr(CO)2(SPAr)]2
(cis-7) as dark brown crystalline solids (14%), and its isomer trans-7 as dark red crystals
(5%), together with 9 (4%) and 10 (11%). The ambient-temperature reaction of [Cp*Cr(CO)3]2
(1*; Cp* = η5-C5Me5) yielded the Cp* analogues of 4, 5, 9, and 10, i.e., 4*, 5*, 9*, and 10*
with yields of 51, 17, 6, and 8%, respectively. The thermolysis of Cp*2Cr2(CO)5(S2PAr) (4*)
resulted in the isolation of Cp*Cr(CO)2(SP(H)Ar) (6*), Cp*2Cr2(CO)4(SPAr) (8*), and Cp*2Cr2(S2P(O)Ar)2 (5*) with yields of 7, 14, and 13%, respectively. A NMR spectral study
demonstrated that thermolytic degradation of complex 3 or its reaction with sulfur or
Lawesson's reagent (2) led to the formation of cis-7; cis- and trans-7 were found to interconvert
under elevated temperatures, giving 4:1 equilibrium mixtures at 80 °C; both isomers react
with 1 to re-form 3. The solid-state structures of all the above-mentioned complexes have
been characterized by single-crystal X-ray diffraction analysis. Complexes 3 and 8* contain
the phosphinothioylidene ligand in different coordination modes. The analogous structures
of complexes 4/4* reveal a bridging dithiophosphorane ligand, being η2(S,S‘) coordinated to
a Cp/Cp*Cr(CO)2 moiety and η1(P) coordinated to a Cp/Cp*Cr(CO)3 moiety. The similar
molecular structures of 5 and 5* contain an eight-membered ring, comprising two CpCr/Cp*Cr units and two [S2P(O)Ar] moieties. Complexes 6/6* contain a rare η2-arylthioxophosphane ligand. The complexes cis- and trans-7 are conformers of a P−P-bonded dimer.