Subject: MM for Transition Metal Cpds

From: [email-masked] (Bersuker)
Date: Mon, 10 Jan 94 14:16:11 CST

Concerning your message with regard to molecular mechanics (MM) 1/04/94,
I should like to essentially disagree with what is suggested until now for MM
with transition metals because in principle the MM methods are a priori
INVALID in the case of TM compounds. The reason is in the strong heterogeneity
effects introduced by d electrons in the approximately homogeneous organic
system formed by sp atoms, which results in nontransferability of the bond
characteristics, ligand excitation by coordination, and electron-conformational
effects. We have an Abstract on this subject sent to the 15 Austin Symposium on
Molecular Structure and I have a book on Electronic Structure of TM compounds
to be published by Plenum.
Isaac B. Bersuker, U of Texas at Austin, Chemistry, Austin, TX 78712.

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From: [email-masked]
Date: Mon, 10 Jan 1994 17:59:16 -0600 (CST)

Hi Isaac,

	I had another thought about your e-mail over the weekend which I
would like to get an opinion from you and the others on the net who might
have some experience in this area.  My questions is simply this - What
about the application about MM to d**0 complexes (i.e., those in their
highest available formal oxidation state)?  The chemistry of d**0
complexes (e.g., Zr(IV), Ta(V), W(VI), etc.), organometallics in 
particular, has attracted much interest from experimentalists due to their
remarkable reactivity, including C-H activation.  Are the aforementioned
problems mitigated to some extent?  What about the combination of MM
and Hartree-Fock based methods, where MM is used for the substituents on the
ligands and the metal and its inner coordination sphere is treated with HF
methods (as an example)?  The large size of many of the ancillary ligands
used to engender some degree of kinetic and thermodynamic stability to
the d**0 complexes suggests that novel approaches may be necessary.
	I would be interested in some view points on this.

			Tom Cundari
			Asst. professor
			Dept. of Chemistry
			Memphis State University