Nucleophilic Addition of Phosphines to Carbonyl Groups. Isolation of 1-Hydroxy Phosphonium and 1-(Trimethylsilyloxy) Phosphonium Salts and the Crystal Structure of (1-Hydroxy-1-methylethyl)triehtylphosphonium Bromide

Article abstract of DOI:10.1021/jo00296a020

1-Hydroxy phosphonium salts and 1-(trimethylsilyloxy) phosphonium salts can be isolated by nucleophilic addition of a small basic phosphine (PMe3 or PEt3) to the carbonyl carbon of aldehydes or ketones in the presence of Br2-acetone (a source of anhydrous HBr), anhydrous acids, or chlorotrimethylsilane as trapping agents.The crystal structure of <(CH3)2C(OH)(PEt3)>Br, Ib, was determined through C-ray diffraction.Ib crystallizes in the monoclinic system, space group P2₁/n with lattice constant a = 7.304(3) Angstroem, b = 12.004(4) Angstroem, c = 14.164(5) Angstroem,β = 93.33(3) deg, and Z = 4.Least-squares refinement of the structure led to a R (R_w) factor of 0.042 (0.043) for 732 unique reflections of I > 3?(I) and for 62 least-squares variables.The phosphorous atom and all carbon atoms adopt sp³ hybridization.The C-O bond distance of 1.429(10) Angstroem indicates a normal C-O single bond; however, the P-C bond to the carbonyl derived carbon (1.877(10) Angstroem) is significantly longer than the other P-C bonds (1.80(1) Angstroem av).