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 degrees C. Under similar conditions the ethyl analogue (Et)CgPH 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 Br-2. 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 = Pr-i; (b) treatment of CgP(BH3)Li with RX followed by borane deprotection with Et2NH, which has been used for R = Pr-i, benzyl, n-C20H41; (c) treatment of CgPBr with RMgX, which has been used for R = Pr-i, Me. The complexes [PtC12(CgPH)(2)] (1), [PdCl2(CgPH)(2)] (2), [PdCl2(CgPR)(2)] (where R = Pr-i (3a), Cy (3b)), and [PtCl2(CgPR)(2)] (where R = Pr-i (4a), Cy (4b), n-C20H41 (4c)) are described. The crystal structures of CgPH, CgPCl, [CgP(CH2Ph)(2)]Br, CgP(n-C20H41), and complexes 1, 3b, and 4c are reported. From the v(CO) values for trans-[RhCl(CO)(CgPX)(2)], the sigma-donor/pi-acceptor properties of CgPX are in the order X = Pr-i > Me > Ph > H > Cl.