Organometallic Solutions: #18

18.* (1992 2 5) For each of the following, A. Which compounds could dimerize? B. Which compounds are not coordinatively saturated? C. For which compounds is cis-trans isomerism possible? D. Which compounds have more than 18 electrons?

 

Re(CO)5

(L)2Pt(R)2 ; R=CH3 , L=Bu3P

Mn(CO)5(CH3)

Fe(CO)5

Cp2Co (Cp=C5H5)

Cp2Ni

Cp2Fe+

L3Pt

 

A. Simply count the d electrons. Complexes with 17 d electrons can be expected to dimerize. This includes #1. #7 could probably dimerize if it existed, although steric crowding and charge repulsion would make it rather difficult. #5 is also correct (see D)

B. #2 and #8 both have sixteen electrons. (17 electron complexes are not considered unsaturated.)

C. #2, being square planar, can have cis or trans isomers. However, it is achiral because it is planar.

D. #6 has 20 valence electrons. #5 does not really have more than 18. Cp- can donate 2, 4, or 6 electrons. Here one would donate 6 and the other would donate 4 to give a 17-electron complex.