Table 1. Selected X-ray Crystallographic and Calculated Structural Parameters for 2, 4, 22, and 23.

	2		4	22	23
	X-ray	Calcd	Calcd	Calcd	Calcd
d(Ni−C), Å	1.900(7)	1.930	1.962	1.963	1.933
		1.930	1.962	1.962	1.957
		1.930	1.962	1.963	1.957
		1.930	1.963	1.963	1.932
∠C−Ni−C, deg (cis)	90	90.01	91.96	90.29	87.50
	90	90.00	92.00	90.40	92.79
	90	90.02	91.95	90.34	87.50
	90	89.96	91.97	90.33	87.10
∠C−Ni−C, deg (trans)	180	179.77	158.57	171.16	178.01
	180	179.82	158.67	171.16	176.86
d(Ccarbene−N), Å	1.331(6)	1.366	1.391	1.377	1.370
		1.366	1.404	1.381	1.370
∠N−Ccarbene−N, deg	102.6(6)	104.2	101.5	103.0	104.7