Flexible Coordination of Diphosphine Ligands Leading to cis and trans Pd(0), Pd(II), and Rh(I) Complexes

A series of diphosphine ligands iPr2P–C6H4–X–C6H4–PiPr2 (for ligand L1, X = CH2; for ligand L2, X = CH2CH2) was investigated to determine the preference for cis/trans coordination
to palladium(0), palladium­(II), and rhodium­(I). Increasing the length
of the bridging alkyl backbone from one to two carbons changes the
geometry of the resulting palladium­(II) complexes, with L1 coordinating preferentially cis, while L2 coordinates
in a trans fashion. Coordination to Pd(0) leads to L1Pd­(dba)
and L2Pd­(dba), in which both ligands accommodate a P–M–P
angle close to 120°. L2 was found to coordinate cis
in a rhodium­(I) complex ([L2Rh­(nbd)]­[BF4], where
nbd = norbornadiene).

本研究针对一系列双膦配体（diphosphine ligands）iPr2P–C6H4–X–C6H4–PiPr2（其中配体L1的X为CH2，配体L2的X为CH2CH2）展开探究，以明确其与钯(0)、钯(II)及铑(I)配位时的顺/反式配位偏好。将桥联烷基骨架的碳链长度从1个增至2个，会改变所得钯(II)配合物的几何构型：L1优先以顺式方式配位，而L2则采取反式配位构型。与零价钯配位后可得到L1Pd(dba)与L2Pd(dba)，这两种配合物中两种配体的P–M–P键角均接近120°。研究发现，在铑(I)配合物[L2Rh(nbd)][BF4]（其中nbd为降冰片二烯（norbornadiene））中，L2以顺式方式配位。