ROTATIONAL BARRIERS IN DIPHENYLMETHYL ANIONS STABILIZED BY TRIMETHYLSILYL AND TRICARBONYLCHROMIUM(0) MOIETIES.

Article abstract of DOI:10.1021/ja00359a011

A series of diphenylmethyl anions has been prepared in which the phenyl rings bear pi -bonded Cr(CO)//3 groups and/or a trimethylsilyl moiety. Variable-temperature **1**3C NMR studies on these compounds have allowed the evaluation of the barriers to phenyl rotation. It is shown that a pi -bonded Cr(CO)//3 group stabilizes the negative charge much more efficiently than does a p-SiMe//3 functionality. However, when the Me//3Si substituent is bonded directly to the alpha -carbon atom, the charge preferentially resides on the silicon, allowing the ( pi -Cr(CO)//3 minus C//6H//5) groups to rotate apparently unhindered.