Transition metals stabilized

As previously shown , transition-metal stabilized carbenes cannot be used as sources of free carbenes, due to their chemical inertness. However, selected reagents can operate specific transformations on these complexes (Scheme 11) ... 

Dr. Halpem But all that is necessary to explain your observation is that this intermediate be fairly long lived and then that two of these ultimately combine. There is some evidence for a similar phenomenon in the case of free radicals. J. K. Kochi and F. F. Rust (9) have shown that transition metal ions, among them Fe(II), catalyze the recombination of free radicals by what appears to be substantially this kind of mechanism—i.e., the transition metal stabilizes the radical against abstraction presumably by forming a complex with it, which then lives long enough to combine with another one. 

Pearson, A J 1987, Transition Metal-Stabilized Carbocations in Organic Synthesis, in Hartley, F R (ed), Chemistry of the Metal-Carbon Bond, Vol 4, chapter 10, Wiley Chichester, UK. 

Varghese V, Saha M, Nicholas KM (1988) Org Synth 67 141 Nicholas KM (1987) Acc Chem Res 20 207 Caffyn AJM, Nicholas KM (1995) Transition metal alkyne complexes transition metal stabilized propargyl system. In Abel EW, Stone FGA, Wilkinson G (eds) Comprehensive organometallic chemistry II, vol 12. Pergamon Press, Oxford, p 685 Schreiber SL, Klimas MT, Sammakia T (1987) J Am Chem Soc 109 5749 Nakamura T, Matsui T, Ta-nino K, Kuwajima I (1997) J Org Chem 62 3032... 

Two transition metal stabilized germyl cations, 10 and 11 , have been reported. In the first one the strongly pyramidalized cationic germanium center is bonded to two iron atoms and one t-Bu group, and is stabilized by the coordination to DMAP. The second one has a planar cationic germanium bonded to two tungsten atoms and one methyl group. 

Carbenes are formally divalent carbon species and as such are very reactive. Certain transition metals stabilize the carbene. The metal arbene complexes which result, some of which are stable, are called "carbenoids . since an actual carbene is no longer present. 

Lockwood, R. F., Nicholas, K. M. Transition metal-stabilized carbenium ions as synthetic intermediates. I. a-[(Alkynyl)dicobalt hexacarbonyl] carbenium ions as propargylating agents. Tetrahedron Lett. 1977, 4163-4166. 

Nicholas, K. M., Caffyn, A. J. M. Transition metal alkyne complexes Transition metal-stabilized propargyl systems, in Comprehensive Organometallic Chemistry II. (eds. Abel, E. W., Stone, F. G. A.,Wilkinson, F.), 12, 685-702 (Oxford, 1995). 

Muller, T. J. J. Stereoselective propargylations with transition-metal-stabilized propargyl cations. Eur. J. Org. Chem. 2001,2021-2033. 

Transition-metal-stabilized carbocations can be generated from functionalized butadieneiron carbonyl or arenechromium tricarbonyl complexes [92], Reactions of such carbocations formed from chiral complexes have been studied, but low selectivities are usually observed [526, 528, 535]. However, chromium tricarbonyl complexes derived from ephedrine 5.66 suffer cyclization in acidic medium. After decomplexation, c/s-tetrahydroquinolines are formed with a high diastereo-and enantioselectivity [540,542] (Figure 5.44). 

Homoatomic dusters with six, seven, eight, or more than ten vertices have not yet been isolated from solution, although both gas-phase experiments and theoretical investigations have predicted a remarkable stability for the stannaspherene [Sni2] and the plumbaspherene [Pbi2] [32]. Octahedral [Es] " clusters have only been isolated as transition metal-stabilized spedes [EMfCOjs] (E = Ge and Sn and M = Cr, Mo or W). These display an almost-perfect E octahedron, with each E atom coordinated to an M(CO)s fragment [33]. 

Main Group alkyls can also (3-eliminate (e.g., Eq. 3.2), but this usually happens much more slowly. The reason for this difference is believed to be the greater ability of d-block metals to stabilize the transition states involved. We shall see shortly how in rare cases stable complexes exist in which transition metals stabilize what appear to be intermediate forms between simple alkyls and the hydride alkene product of (3 elimination. 

Miither K, Frohlich R, Miick-Lichtenfeld C, Grimme S, Oestreich M (2011) A unique transition metal-stabilized silicon cation. J Am Chem Soc 133 12442... 

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