Dinuclear Cycloaurated Complexes Containing Bridging (2-Diphenylphosphino)phenylphosphine and (2-Diethylphosphino)phenylphosphine, C6H4PR2 (R = Ph, Et). Carbon-Carbon
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- 作者：Martin A. Bennett ; Suresh K. Bhargava ; David C. R. Hockless ; Lee L. Welling ; and Anthony C. Willis
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：October 30, 1996
- 年：1996
- 卷：118
- 期：43
- 页码：10469 - 10478
- 全文大小：261K
- 年卷期：v.118,no.43(October 30, 1996)
- ISSN：1520-5126
文摘
The digold(I) complexesAu2(![]()
RC="/images/entities/mgr.gif">-C6H4PR2)2[R = Ph (1a), Et (1b)] obtained by treatmentof AuBr(PEt3)with o-LiC6H4PR2undergo addition with halogens or benzoyl peroxide to givemetal-metal bonded digold(II)complexesAu2X2(
r.gif">-C6H4PR2)2[R = Ph, Et; X = I (2a, 2b), Br(3a, 3b), Cl (4a, 4b),O2CPh (5a, 5b)], whicharestructurally similar to the bis(ylide) complexesAu2X2{r.gif">-(CH2)2PR2}2.The benzoate ligands in 5b are monodentateand the gold-gold bond length [2.5243(7) Å] is significantlyless than that in the diiodide (2a) [2.5898(6) Å,2.5960(Å) for independent molecules], reflecting the trans influences ofthe axial anionic ligands. The correspondingcomplexesAu2X2(r.gif">-C6H4PR2)2[R = Ph, Et; X = O2CMe (6a,6b), ONO2 (7a, 7b)] aremade from 2-4 and theappropriate silver salt. The axial anionic ligands undergoimmediate scrambling when solutions ofAu2X2(r.gif">-C6H4PR2)2 andAu2Y2(r.gif">-C6H4PR2)2are mixed. The bridgingC6H4PR2 units also scramblerapidly on mixing solutionsofAu2X2(r.gif">-C6H4PPh2)2[X = I (2a), Br (3a)] andAu2X2(r.gif">-C6H4PEt2)2[X = I (2b), Br (3b)], but this occursonlyslowly for X = Cl and not at all for X = O2CPh,O2CMe, or ONO2. Solutions of thediiodo complexes 2a, 2b andthe dibromo complexes 3a, 3b isomerize cleanly tothe digold(I) complexesAu2X2(r.gif">-R2PC6H4C6H4PR2)[R = Ph,Et; X = I (8a, 8b), Br (9a,9b)] containing 2,2'-biphenylyl(diphenylphosphine) or2,2'-biphenylyl(diethylphosphine),respectively, as a consequence of a reductive elimination in which aC-C bond is formed at the expense of twoAu-C bonds. In 8b the Au-Au separation is3.167(1) Å and the phenyl rings of the biphenyl unit arealmostorthogonal. Qualitatively, the rates of isomerization ofAu2X2(r.gif">-C6H4PR2)2toAu2X2(r.gif">-R2PC6H4C6H4PR2)are inthe order R = Ph > Et; X = I > Br >> Cl; isomerization does notoccur for X = O2CPh, O2CMe, orONO2. Therates of thermal isomerization of 2a and 3a arefirst order in complex, only slightly sensitive to solvent polarity,and,for 2a, inhibited by iodide ion. It is suggested thatreversible loss of halide ion initiates aryl group transferbetweenthe gold atoms, thus allowing reductive elimination of Au-C bonds totake place at one center. Treatment of 2aor3a with an excess of iodine or bromine gives initiallydigold(III) complexescis,trans-Au2X4(r.gif">-C6H4PPh2)2[X = I(14), Br (15)], which are in equilibrium withmonomersAuX2(C6H4PPh2)[X = I (16), Br (17)], as shown by31PNMR spectroscopy. These species isomerize at room temperature byinternal electrophilic cleavage of their Au-Cbonds to give stable gold(I) complexes of(2-halogenophenyl)diphenylphosphine,AuX(o-XC6H4PPh2)[X = I (12),Br (11)].
r.gif">-C6H4PR2)2[R = Ph, Et; X = I (2a, 2b), Br(3a, 3b), Cl (4a, 4b),O2CPh (5a, 5b)], whicharestructurally similar to the bis(ylide) complexesAu2X2{r.gif">-(CH2)2PR2}2.The benzoate ligands in 5b are monodentateand the gold-gold bond length [2.5243(7) Å] is significantlyless than that in the diiodide (2a) [2.5898(6) Å,2.5960(Å) for independent molecules], reflecting the trans influences ofthe axial anionic ligands. The correspondingcomplexesAu2X2(r.gif">-C6H4PR2)2[R = Ph, Et; X = O2CMe (6a,6b), ONO2 (7a, 7b)] aremade from 2-4 and theappropriate silver salt. The axial anionic ligands undergoimmediate scrambling when solutions ofAu2X2(r.gif">-C6H4PR2)2 andAu2Y2(r.gif">-C6H4PR2)2are mixed. The bridgingC6H4PR2 units also scramblerapidly on mixing solutionsofAu2X2(r.gif">-C6H4PPh2)2[X = I (2a), Br (3a)] andAu2X2(r.gif">-C6H4PEt2)2[X = I (2b), Br (3b)], but this occursonlyslowly for X = Cl and not at all for X = O2CPh,O2CMe, or ONO2. Solutions of thediiodo complexes 2a, 2b andthe dibromo complexes 3a, 3b isomerize cleanly tothe digold(I) complexesAu2X2(r.gif">-R2PC6H4C6H4PR2)[R = Ph,Et; X = I (8a, 8b), Br (9a,9b)] containing 2,2'-biphenylyl(diphenylphosphine) or2,2'-biphenylyl(diethylphosphine),respectively, as a consequence of a reductive elimination in which aC-C bond is formed at the expense of twoAu-C bonds. In 8b the Au-Au separation is3.167(1) Å and the phenyl rings of the biphenyl unit arealmostorthogonal. Qualitatively, the rates of isomerization ofAu2X2(r.gif">-C6H4PR2)2toAu2X2(r.gif">-R2PC6H4C6H4PR2)are inthe order R = Ph > Et; X = I > Br >> Cl; isomerization does notoccur for X = O2CPh, O2CMe, orONO2. Therates of thermal isomerization of 2a and 3a arefirst order in complex, only slightly sensitive to solvent polarity,and,for 2a, inhibited by iodide ion. It is suggested thatreversible loss of halide ion initiates aryl group transferbetweenthe gold atoms, thus allowing reductive elimination of Au-C bonds totake place at one center. Treatment of 2aor3a with an excess of iodine or bromine gives initiallydigold(III) complexescis,trans-Au2X4(r.gif">-C6H4PPh2)2[X = I(14), Br (15)], which are in equilibrium withmonomersAuX2(C6H4PPh2)[X = I (16), Br (17)], as shown by31PNMR spectroscopy. These species isomerize at room temperature byinternal electrophilic cleavage of their Au-Cbonds to give stable gold(I) complexes of(2-halogenophenyl)diphenylphosphine,AuX(o-XC6H4PPh2)[X = I (12),Br (11)].