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Metal Alkyl Complexes


Structure and Bonding

Synthesis of Metal Alkyl Complexes

Decomposition Modes of Metal Alkyls

Empirical order of stabilities

The factors discussed above all influence the stability of metal alkyl complexes. We can come up with some experimental observations about the relative stabilities of different alkyl ligands:

  1. 1-norbornyl > benzyl > trimethylsilyl > neopentyl > Ph ~ Me >> Et (1o R) > 2, 3o R

    impossible reaction

    Notice that norbornyl not only has a difficult time approaching the metal center, but that the olefin that would be generated would be highly strained (and violate Bent's rule).

  2. Fluoroalkyl > alkyl (i.e. -CnF2n+1 > -CnH2n+1)

    CF bonds are very strong (120-130 kcal/mol vs. 98-104 kcal/mol for alkyl C-H).

  3. Chelating (metallacycles) > nonchelating (acyclic)

    a platinacycle

    The dialkyl shown on the left decomposes at 110 oC with kdec = 1.0 s-1. In contrast, the metallacycle has k = 5.3 x 10-3 s-1. The beta-hydrogen has a close approach to the metal in the dialkyl case, but not the metallacycle.

  4. 3rd row > 2nd row > 1st row transition metals.

    Os dialkyl vs. Fe

  5. Strong electron-donating ligands increase stability.

    CO vs PR3

    The carbonyl ligand reduces electron density on the metal through pi-backbonding, in contrast to the phosphine ligand, which is a good sigma donor.

dividing line

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This page was last updated Tuesday, March 31, 2015
This document and associated figures are copyright 1996-2016 by Rob Toreki or the contributing author (if any) noted above. Send comments, kudos and suggestions to us by email. All rights reserved.