“…However, two-coordinate transition-metal complexes, [R*MFe(η 5 -C 5 H 5 )(CO) 2 ] (M = Fe, Mn, Cr; R* = -C 6 H-2,6-Ar 2 -3,5-i Pr 2 where Ar = -C 6 H 2 -2,5,6-i Pr 3 ), were synthesized and isolated. 61 As might be apparent from Figure 29, the bulky R* group surrounds the two-coordinate M atom and blocks the formation of any third bond to M. X-ray crystal analysis showed that the metalmetal bond distances are 2.393 ¡ for FeFe, 2.451 ¡ for MnFe, and 2.489 ¡ for CrFe. These metalmetal bond distances are much shorter than those of the known complexes with unsupported FeFe (2.6873.138 ¡), MnFe (2.6012.843 ¡), and CrFe Figure 29b.…”