DINUCLEAR CYCLOAURATED COMPLEXES CONTAINING BRIDGING (2-DIPHENYLPHOSPHINO)PHENYLPHOSPHINE AND (2-DIETHYLPHOSPHINO)PHENYLPHOSPHINE, C(6)H(4)PR(2) (R=PH, ET), CARBON-CARBON BOND FORMATION BY REDUCTIVE ELIMINATION AT A GOLD(II)-GOLD(II) CENTER
Ma. Bennett et al., DINUCLEAR CYCLOAURATED COMPLEXES CONTAINING BRIDGING (2-DIPHENYLPHOSPHINO)PHENYLPHOSPHINE AND (2-DIETHYLPHOSPHINO)PHENYLPHOSPHINE, C(6)H(4)PR(2) (R=PH, ET), CARBON-CARBON BOND FORMATION BY REDUCTIVE ELIMINATION AT A GOLD(II)-GOLD(II) CENTER, Journal of the American Chemical Society, 118(43), 1996, pp. 10469-10478
The digold(I) complexes Au-2(mu-C(6)H(4)PR(2))(2) [R = Ph (1a), Et (1b
)] obtained by treatment of AuBr(PEt(3)) with o-LiC(6)H(4)PR(2) underg
o addition with halogens or benzoyl peroxide to give metal-metal bonde
d digold(II) complexes Au(2)X(2)(mu-C(6)H(4)PR(2))(2) [R = Ph, Et; X =
I (2a, 2b), Br (3a, 3b), Cl (4a, 4b), O(2)CPh (5a, 5b)], which are st
ructurally similar to the bis(ylide) complexes Au(2)X(2){mu-(CH2)(2)PR
(2)}(2). The benzoate ligands in 5b are monodentate and the gold-gold
bond length [2.5243(7) Angstrom] is significantly less than that in th
e diiodide (2a) [2.5898(6) Angstrom, 2.5960 (A) for independent molecu
les], reflecting the trans influences of the axial anionic ligands. Th
e corresponding complexes Au(2)X(2)(mu-C(6)H(4)PR(2))(2) [R = Ph, Et;
X = O(2)CMe (6a, 6b), ONO2 (7a, 7b)] are made from 2-4 and the appropr
iate silver salt. The axial anionic ligands undergo immediate scrambli
ng when solutions of Au(2)X(2)(mu-C6H4- PR(2))(2) and Au2Y2(mu-C(6)H(4
)PR(2))(2) are mixed. The bridging C(6)H(4)PR(2) units also scramble r
apidly on mixing solutions of Au(2)X(2)(mu-C(6)H(4)PPh(2))(2) [X = I (
2a), Br (3a)] and Au(2)X(2)(mu-C(6)H(4)PEt(2))(2) [X = I (2b), Br (3b)
], but this occurs only slowly for X = Cl and not at all for X = O(2)C
Ph, O(2)CMe, or ONO2. Solutions of the diiodo complexes 2a, Zb and the
dibromo complexes 3a, 3b isomerize cleanly to the digold(I) complexes
Au(2)X(2)(mu-R(2)PC(6)H(4)C(6)H(4)PR(2)) [R = Ph, Et; X = I (8a, 8b),
Br (9a, 9b)] containing 2,2'-biphenylyl(diphenylphosphine) or 2,2'-bi
phenylyl(diethylphosphine), respectively, as a consequence of a reduct
ive elimination in which a C-C bond is formed at the expense of two Au
-C bonds. In 8b the Au-Au separation is 3.167(1) Angstrom and the phen
yl rings of the biphenyl unit are almost orthogonal. Qualitatively, th
e rates of isomerization of Au(2)X(2)(mu-C(6)H(4)PR(2))(2) to Au(2)X(2
)(mu-R(2)PC(6)H(4)C(6)H(4)PR(2)) are in the order R = Ph > Et; X = I >
Br > > Cl; isomerization does not occur for X = O(2)CPh, O(2)CMe, or
ONO2. The rates of thermal isomerization of 2a and 3a are first order
in complex, only slightly sensitive to solvent polarity, and, for 2a,
inhibited by iodide ion. It is suggested that reversible loss of halid
e ion initiates aryl group transfer between the gold atoms, thus allow
ing reductive elimination of Au-C bonds to take place at one center. T
reatment of 2a or 3a with an excess of iodine or bromine gives initial
ly digold(III) complexes cis,trans-Au(2)X(4)(mu-C(6)H(4)PPh(2))(2) [X
= I (14), Br (15)], which are in equilibrium with monomers AuX(2)(C(6)
H(4)PPh(2)) [X = I (16), Br (17)], as shown by P-31 NMR spectroscopy.
These species isomerize at room temperature by internal electrophilic
cleavage of their Au-C bonds to give stable gold(I) complexes of (2-ha
logenophenyl)diphenylphosphine, AuX(o-XC(6)H(4)PPh(2)) [X = I (12), Br
(11)].