Synthetic and structural studies on (η5:η5-fulvalene)bimetallic compounds derived from (η5:η5-fulvalene)dithallium

Article abstract of DOI:10.1016/0022-328X(90)85134-K

A reaction between halide-free solutions of dihydrofulvalene and thallium ethoxide has produced (η⁵ : η⁵-fulvalene)dithallium (1) in 85-100percent yield.Reactions of 1 with carbonyl halides of cobalt, rhodium, iridium, manganese and rhenium produce corresponding homobimetallic fulvalene metal carbonyls (2, 5, 9-11) in yields of 52-94percent.The rhodium complex (η⁵ : η⁵-C10H8)Rh2(CO)4 (5) reacted with trimethylamine-N-oxide dihydrate to form a tricarbonyl derivative (η⁵ : η⁵-C10H8)Rh2(μ-CO)(CO)2 (6) that contained a bridging carbonyl group and a rhodium-rodium bond.The bridging carbonyl substituent could be replaced by a bridging methylene group by reaction of 6 with N-methyl-N-nitrosourea.Tetra(η²-ethylene)-, bis(η⁴-1,2,5,6-cyclooctadiene)-, and bis(η⁴-1,2,5,6-cyclooctatetraene)(η⁵ : η⁵-fulvalene)dirhodium (12-14) have been prepared in high yields by reactions of 1 with the corresponding chloro(diolefin)rhodium dimers.Variable temperature 1H NMR studies on the tetraethylene complex 12 demonstrated that the ethylene ligands are fluxional, with ΔG⁺ 65 +/- 1 KJ/mol.Photolysis of 14 with two equivalents of (η²-C2H4)2(η⁵-C5H5)Rh has afforded the tetranuclear complex bis <(η⁵-cyclo-pentadienyl)rhodium(μ-cyclooctatetraene)>(η⁵ : η⁵-fulvalene)dirhodium (15) in 27percent yield.The single crystal X-ray structures of 2,5,10, and 12 have been carried out.Each consists of an η⁵ : η⁵-fulvalene dianion bridging two metal centers which lie on opposite sides on the fulvalene plane.In each case the formula unit resides around a crystallographic center of inversion. 2 and 5 are isostructural crystallizing in the monoclinic space group P2₁/c with a 7.938(6), b 8.223(7),c 10.884(8) Angstroem, β 109.34(4)deg, and D_calc 1.77 gcm^-3 for Z = 2 (2) and a 8.149(1), b 8.420(1), c 10.498(4) Angstroem, β 107.27(2)deg and D_calc 2.15 gcm^-3 for Z = 2 (5).The average M-C(η⁵) and M-CO distances are Co-C(η⁵) 2.10(2) Angstroem, Co-CO 1.734(6) Angstroem (2) and Rh-C(η⁵) 2.27(3) Angstroem, Rh-CO 1.864(3) Angstroem (5). 10 is monoclinic P2₁/n with a 10.366(6), b 6.986(4), c 11.910(5) Angstroem, β 115.07(4)deg and D_calc 1.73 gcm^-3 for Z = 2.The average Mn-C(η⁵) and Mn-CO distances are 2,115(5) and 1.802(6) Angstroem, respectively. 12 is triclinic, P1, with a 8.068(1), b 9.998(4), c 11.509(3) Angstroem α 67.48(2), β 69.01(2), χ 80.51(3)deg and D_calc 1.85 gcm^-1 for Z = 2.There are two unique molecular units each residing around a crystallographic center of inversion.The two differ by a small rotation of the Rh(C2H4)2 fragments.The average Rh-C(η⁵) and Rh-C(η²) separations are 2.25(3) and 2.129(9) Angstroem, respectively.