Metal cleavage

This protective group was used to improve the directed ortho metallation. Cleavage... 

Isomerization of 2,2,4,4-tetramethyloxetane on platinum, palladium and rhodium catalysts at 100 °C to 4,4-dimethyl-2-pentanone has been observed (equation 69). A mechanism involving noble metal cleavage of C—O and a 1,3-methyl shift has been proposed (79CC139). 

Tertiary alkyl and cycloaliphatic phosphines do not undergo alkali metal cleavage however, (aryl)3 (alkyl) P ( = 1, 2) are cleaved25 by Li/THF to give LiP(aryl)2 (alkyl) and aryllithium. Although this appears to be an attractive route to LiP(alkyl)2, it has not been widely exploited. Somewhat anomalously, PhEt2P and K produce KPEtPh and not KPEt2.27... 

Direct comparison of the rate of cleavage of an allyl-metal bond with that of an ethyl-metal bond is possible in three particular cases, and it will be shown later that the ratio of the second-order rate coefficients for allyl-metal cleavage to ethyl-metal cleavage are as shown below. 

Nucleophilic cleavage of the lead-lead bond is one of the few ways to form plumbyl anions (equations 30, 37 and 38)45,51,52, but in the case of a sterically hindered and thus weak lead-lead bond, a metal-metal cleavage is required (equation 39)45,51-53. 

Alkyne ligands have been removed from metal complexes intact, in oxidized form, and in reduced form. In spite of accomplishing alkyne-metal cleavage with different reagents in specific cases, there is no general method for systematically separating an alkyne ligand from a d4 metal center. 

Monti and his co-workers have successfully demonstrated not only the efficiency of intramolecular ketocarbene capture in the production of tricyclo[3.3.0.02-8 ]-octan-3-one (27), but also the marked stereoselectivity of its dissolving metal cleavage and ring opening under acidic conditions (Scheme 7).ss Prevailing stereoelec-tronic and thermodynamic factors favor predominant conversion to bicyclo[3.3.0]-octyl end products. 

The phospholyl anions were discovered by Braye and are readily prepared through alkali metal cleavage of the exocyclic phosphorus-carbon bond of phospholes ... 

This salt is prepared by alkali metal cleavage of AsPhs. Its properties are similar to those of KPPh2 2 dioxane, and it must be handled similarly. 

The Li-metal cleavages of Eq. (a) require strenuous conditions, and the organolithiums formed may attack the solvent subsequently. Tetrahydrofuran (THF) is the most efficacious, permitting less severe conditions. Excess Li metal is used. 

The photolysis of Re2(CO)io in the presence of H2 yields a mixture of products including ReH(CO)s, Re3H3(CO)i2, and Re3H(CO)i4. A similar photolysis of Mn2(CO)io and H2 gives MnH(CO)s as the primary isolable product. The key step in a multistep mechanism involves oxidative addition of hydrogen to a 15-electron intermediate, M(CO)4, which is formed by initial metal-metal cleavage followed by CO loss". 

Most group 1 phospholides have been prepared through alkali metal cleavage of a phosphole P-Ph bond and, after destruction of phenyl-derived byproducts (with tert-BuCl AlCl3, etc.), used in situ [3]. However, this convenient method is poorly adapted to sensitive chemistry and effort has been devoted to isolating pure alkali metal phospholides. When not substituted by chromophores, these are colorless, and sometimes pyrophoric materials. 

Keywords Activation, C-C bond, Transition metal, Cleavage, Oxidative addition, P-carbon elimination, Directionality, Homogeneous... 

Interaction of A-B with the 17 e radical MLn leads to formation of the 19 e complex MLn(A-B). According to the simple molecular orbital theory, such 19 e complexes are stabilized by the formation of a half bond between the metal and A-B.1 Much of the reactivity of 17 e radicals keys off these elusive 19 e adducts that can form in rapid associative reactions. The 19 e adduct MLn(A-B) can eject a ligand to form a substituted radical complex via the lower reaction in Scheme 10.1. If the A-B bond is particularly weak, homolysis to A-.V1L, and a free "B radical can occur. The "B radical generated as such may then combine with MLn(A-B) to form B-.V1L, or enter different reaction channels. If the A-B bond is strong, a second mole of radical may be required to break the A-B bond. In that case, an intermediate adduct LnM(A-B)MLn forms and then fragments to A-.V1L, and B-.V1L,. These are the same products obtained in homolytic (single metal) cleavage, but the important difference is that free "B radicals are not formed in the reaction. 

Wells, A. A., Unstable Crack Propagation in Metals-Cleavage and Fast Fracture, Proc. Crack Propagation Symposium, Cranfield (1961), 210-230. 

In the six-carbon intermediate, both the oxygen at C-2 and the newly formed carboxyl group appear to be coordinated to the metal. Cleavage of this intermediate presumably occurs by attack of external water. 

The metal cleavage reaction is an important synthetic approach to the reactive R3PbM derivatives. In turn, these latter compounds are useful intermediates for the preparation of unsymmetrical tetraorganolead compounds. 

During hydrogenolysis of isopropylcyclobutane over the Group VIII noble metals, cleavage of all the ring C—C bonds occurs. Selectivity of cleavage opposite the substituent increased in the series Pd, Pt, Ir, Rh, Ru, but the last three metals also catalysed... 

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