Synthesis, Nujol matrix and solution photochemistry of M(CO)2[η5,η3-C5H 4-C(CH3)2-C5H6] (where M=Cr or Mo): Molecular structures

Article abstract of DOI:10.1016/S0022-328X(99)00118-7

Reaction of chromium or molybdenum carbonyl with 2,2-bis(cyclopentadienyl)propane yields mixtures of products including M₂(CO)₆[η⁵,η⁵-C ₅H₄-C(CH₃)₂-C₅H ₄], M₂(CO)₆[η⁵-C₅H ₄-C(CH₃)₂-C₅H₄] ₂, and the title compounds, M(CO)₂[η⁵,η³-C₅H ₄-C(CH₃)₂-C₅H₆], in which an η³-pentenyl group is tethered to the η⁵-cyclopentadienyl (Cp) group by a 2,2-propyl linkage. Although several isomers are possible for the cyclopentenyl groups, chromium and molybdenum appear to form only single, but unique isomers. Photolysis of M(CO)₂[η⁵,η³-C₅H ₄-C(CH₃)₂-C₅H₆], M=Cr or Mo, in Nujol glass at ca. 77 K has been found to be wavelength-dependent with low energy photolyses resulting in η³→η¹ transformations while higher energy photolyses result in loss of carbon monoxide. Solution photolysis of the molybdenum derivative with triphenylphosphine yields as a first product Mo(CO)₂[P(C₆H₅)₃][η ⁵,η¹-C₅H₄-C(CH₃) ₂-C₅H₆], which undergoes decomposition upon work-up to yield both starting material, and Mo(CO)[P(C₆H₅)₃][η⁵,η ³-C₅H₄-C(CH₃)₂-C ₅H₆]. The molecular structures of three compounds have been determined: Mo(CO)₂[η⁵,η³-C₅H ₄-C(CH₃)₂-C₅H₆]: monoclinic, P2₁/c, a=8.2767(4), b=19.875(1), c=7.960(1) A, β=96.720(6)°, V=1300.4(1) A³, Z=4, R(F)=2.82; Cr(CO)₂[η⁵,η³-C₅H ₄-C(CH₃)₂-C₅H₆]: monoclinic, P2₁/c, a=9.960(1), b=9.1015(6), c=13.997(1) A, β=92.460(9)°, V=1267.7(2) A³, Z=4, R(F)=4.67; Mo(CO)[P(C₆H₅)₃][η⁵,η ³-C₅H₄-C(CH₃)₂-C ₅H₆]: monoclinic, P2₁/c, a=7.939(1), b=22.381(3), c=15.050(2) A, β=103.55(1)°, V=2599.8(5) A³, Z=4, R(F)=4.01.