Equilibration between a phosphine-cobalt complex and an analogous complex containing an N-heterocyclic carbene: The thermodynamics of a phosphine-carbene exchange reaction

被引：75

作者：

Simms, RW ^{[1
]}

Drewitt, MJ ^{[1
]}

Baird, MC ^{[1
]}

机构：

[1] Queens Univ, Dept Chem, Kingston, ON K7L 3N6, Canada

来源：

ORGANOMETALLICS | 2002年 / 21卷 / 14期

关键词：

D O I：

10.1021/om020110+

中图分类号：

O61 [无机化学];

学科分类号：

070301 ; 081704 ;

摘要：

The reaction of CpCo(PPh3)Me-2 with the N-heterocyclic carbene 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) does not result in complete substitution of the PPh3, as expected, but rather in an equilibrium mixture of CpCo(PPh3)Me-2, IPr, CpCo(IPr)Me-2, and PPh3. Determination of the equilibrium constants for this unusual reaction over the temperature range 30-50 degreesC shows that DeltaHdegrees = -24.4 +/- 1.7 kJ mol(-1), DeltaSdegrees = -65.8 +/- 5.5 J mol(-1) K-1, and thus that it is entropy factors arising from steric crowding in CpCo(IPr)Me-2 that prevent complete substitution. Evidence for steric crowding is found in a comparison with the crystal structures of CpCo(PPh3)Me-2, CpCo(IPr)Me-2, and CpCo(IPr)(CO). The smaller, more basic PMe3 does displace IPr completely from CpCo(IPr)Me-2.

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页码：2958 / 2963

页数：6

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