The effect of one valence electron: contrasting (PNP)Ni(CO) with (PNP)Ni(NO) to understand the half-bent NiNO unit.
Reaction of a (PNP)Ni radical with NO finishes in the time of mixing to form a 1:1 adduct with a NO stretching frequency of 1654 cm (-1). NMR data of this diamagnetic product indicate C 2 v symmetry, which is contradicted by the X-ray structure, which shows it to be nonplanar at Ni, with a geometry intermediate between planar and tetrahedral; the planar geometry is thus the transition state for fluxionality giving time-averaged C 2 v symmetry. The X-ray structure, together with DFT calculations, reveals that the "half-bent" NiNO unit and the intermediate coordination geometry result from a Ni --> NO charge transfer, which has a nonintegral value, resulting in a continuum between NO (+) (hence Ni (0)) and NO (-) (hence Ni (II)). This is related to the nonaxially symmetric character of the Ni --> NO back-donation caused by the (PNP) environment on Ni. Steric effects of ( t )Bu and even chelate constraints are ruled out as the cause of the unusual electronic and structural features.
Fullmer
Benjamin C
BC
Department of Chemistry, Indiana University, Bloomington, IN 47405, USA.
Pink
Maren
M
Fan
Hongjun
H
Yang
Xiaofan
X
Baik
Mu-Hyun
MH
Caulton
Kenneth G
KG