General Routes to Alkyl Phosphatrioxaadamantane Ligands

The secondary phosphine CgPH (CgP = 6-phospha-2,4,8-trioxa-1,3,5,7-tetramethyladamantyl group) is made in 50% yield by a modification of the literature method (avoiding high pressures of PH3) by bubbling PH3 through an acidified solution of 2,4-pentanedione at 0 °C. Under similar conditions the ethyl analogue EtCgPH is formed from 3,5-heptanedione in 75% yield. The halophosphines CgPCl and CgPBr are made by treatment of CgPH with N-halosuccinimide. CgPBr is also made by treatment of CgPH with Br2. Three methods are described for the synthesis of CgPR, where R = alkyl: (a) the previously reported acid-catalyzed condensation reaction of RPH2 with 2,4-pentanedione, which has been extended to R = iPr; (b) treatment of CgP(BH3)Li with RX followed by borane deprotection with Et2NH, which has been used for R = iPr, benzyl, n-C20H41; (c) treatment of CgPBr with RMgX, which has been used for R = iPr, Me. The complexes [PtCl2(CgPH)2] (1), [PdCl2(CgPH)2] (2), [PdCl2(CgPR)2] (where R = iPr (3a), Cy (3b)), and [PtCl2(...