EXPERIMENTAL AND THEORETICAL-STUDIES ON THE REACTIVITY OF ALPHA-PHOSPHINO ENOLATES - CRYSTAL-STRUCTURES OF [K(18-CROWN-6)][PH2PCH...C(...O)PH] AND [K(KRYPTOFIX-2,2,2)][PH2PCH...C(...O)PH]

Since the potassium salts of the enolates [Ph2PCH-(-O)Ph]- and [Ph2PCH-C(-O)OEt]-were found to be much less reactive toward electrophiles (e.g. CO2, activated alkynes) than the corresponding palladium(II) complexes, e.g. [(CN)Pd{Ph2PCH-C(-O)OEt}] (CH N = dimethylbenzylamine), we decided to isolate and structurally characterize the complexes [K(18-crown-6)][Ph2PCH-C(-O)Ph] (4), [K(Kryptofix-2,2,2)][Ph2PCH-C(-O)Ph] (5) and [K(18-crown-6)] [Ph2PCH-C(-O)OEt] (6). Complex 4 crystallizes in the triclinic space group P1 with Z = 2 in a unit cell of dimensions a = 13.025(1) angstrom, b = 10.027(1) angstrom, c = 13.976(1) angstrom, alpha = 106.48(1)-degrees, beta = 106.83(1)-degrees, and gamma = 97.98(1)-degrees. The structure was solved and refined using 4584 observed reflections measured on a Siemens AED diffractometer to a final R value of 0.073. Crystals of 5 are triclinic, space group P1BAR with Z = 2 in a unit cell of dimensions a = 14.658(1) angstrom, b = 13.191(1) angstrom, c = 13.3421) angstrom, alpha = 115.89(1)-degrees, beta = 110.33(1)-degrees, and gamma = 65.25(1)-degrees. For 3236 observed reflections R was 0.061. In the structure of complex 4 there are discrete molecules where the oxygen atom from the phosphino enolato ligand interacts with the potassium ion at a distance of 2.630(3) angstrom. The structure of complex 5 consists of complexed cations and anions linked by a weak C17...O7 interaction which could be interpretable as a hydrogen bond. The geometry of the cryptated K+ ions is normal with K...O distances in the range 2.770(4)-2.899(4) angstrom. The geometry of the anion is close to that observed in complex 4, the main difference being due to the significant lengthening of the C37-C38 bond distance [1.404(9) angstrom]. The lengthening along with a more consistent planarity of the O7-C38-C37-P system indicates a more pronounced pi delocalization for the free ligand. Ab initio SCF calculations on the free phosphine enolate anion and on the Li+ and Na+ complexed phosphine enolates were also carried out in order to rationalize their reactivity as a function of their electronic properties. The palladium(II) phosphino enolate complex [(8-mq)Pd{Ph2PCH-C(-O)Ph}] was reacted in THF with AuCl(PPh3) in the presence of AgBF4, affording [(8-mq)Pd{Ph2PCH(AuPPh3)C-(O)Ph}BF4 (8) in which the electrophilic fragment [Au(PPh3)]+ is attached to the carbon atom of the enolate moiety.