Chromium, iron, ruthenium and gold complexes of 3,3-(biphenyl-2,2′-diyl)-1-diphenylphosphino-1-phenylallene: A versatile ligand

Abstract

Successive treatment of 9-(phenylethynyl)fluoren-9-ol ( 1a), with HBr, butyllithium and chlorodiphenylphosphine furnishes 3,3-(biphenyl-2,2′-diyl)-1-diphenylphosphino-1-phenylallene ( 5). Moreover, reaction of 1a directly with chlorodiphenylphosphine yields the corresponding allenylphosphine oxide ( 6). The allenylphosphine ( 5), and Fe 2(CO) 9 initially form the phosphine–Fe(CO) 4 complex, 11, which is very thermally sensitive and readily loses a carbonyl ligand. In the resulting phosphine–Fe(CO) 3 system, 12, the additional site at iron is coordinated by the allene double bond adjacent to phosphorus; the Fe(CO) 3 tripod in 12 exhibits restricted rotation on the NMR time-scale even at room temperature. The corresponding chromium complex, ( 5)-Cr(CO) 5 ( 9), has also been prepared. The gold complexes ( 5)-AuCl ( 13), and [( 5)-Au(THT)] + X −, where (THT) is tetrahydrothiophene, and X = PF 6 ( 14a), or ClO 4 ( 14b), are analogous to the known triphenylphosphine–gold complexes. In contrast, in the (arene)(allenylphosphine)RuCl 2 system the allene double bond adjacent to phosphorus displaces a chloride, and the resulting cationic species undergoes nucleophilic attack by water yielding ultimately a five-membered Ru–P–C C–O ruthenacycle ( 17). Thus, the allenylphosphine ( 5), reacts initially as a conventional mono-phosphine but, when the metal centre has a readily displaceable ligand such as a carbonyl or halide, the allene double bond adjacent to the phosphorus can also function as a donor. X-ray crystal structures are reported for 5, 6, 11, 12, 13, 14a, 14b and 17.