κ1- and κ2-Complexes of Fluorenylidene–Allenyl Phosphines and Phosphine Oxides with Palladium Chloride and Iron Carbonyl: Displacement of Trimethylsilyl by Diphenylphosphino via a Stabilized Carbanion

Abstract

An attempt to prepare 3,3-(biphenyl-2,2′-diyl)-1-diphenylphosphino-1-(trimethylsilyl)allene, 15, by treatment of 3,3-(biphenyl-2,2′-diyl)-1-lithio-1-(trimethylsilyl)allene with chlorodiphenylphosphine led instead to 3,3-(biphenyl-2,2′-diyl)-1,1-bis(diphenylphosphino)allene, 14. The proposed mechanism invokes attack on the trimethylsilyl group in 15 by liberated chloride to form a stabilized anion that reacts with a second molecule of the chlorophosphine. The diphosphine, 14, reacts with di-iron nonacarbonyl to form monodentate 14-Fe(CO)4 and the chelate 14-Fe(CO)3. 9-Ethynyl-9H-fluoren-9-ol and chlorodiphenylphosphine form 3,3-(biphenyl-2,2′-diyl)-1-diphenylphosphinylallene, which is readily deprotonated by triethylamine to generate a stabilized fluorenyl anion, which reacts with a second molecule of the chlorophosphine to furnish 3,3-(biphenyl-2,2′-diyl)-1-diphenylphosphino-1-diphenylphosphinylallene, 26. This bis-phosphine-monoxide (BPMO) reacts with di-iron nonacarbonyl to form initially monodentate P-bonded 26-Fe(CO)4, which loses a carbonyl, allowing the adjacent allene double bond in 26-Fe(CO)3 to coordinate to iron and leave the phosphine oxide uncoordinated. In contrast, the BPMO, 26, and (PhCN)2PdCl2 yield the phosphine-coordinated, chlorine-bridged dimer 34 and also the chelate 35, in which the palladium is linked to both the diphenylphosphino and diphenylphosphinyl groups via phosphorus and oxygen, respectively. Surprisingly, chlorodiphenylphosphine and 1,4-bis(9-hydroxy-9H-fluorenyl)buta-1,3-diyne, 37, do not yield the expected 3,4-bis(phosphinyl)hexa-1,2,4,5-tetraene, 33, but rather the 1-chloro-2-diphenylphosphinocyclobutene, 38, bearing a spiro-bonded fluorenylidene and a fluorenylidene-allene. All new compounds were characterized by 31P NMR spectroscopy and X-ray crystallography.