Phosphines, methylene bridged

Karsch described in 1985 the preparation of the related methylene-bridged phosphine-alane 2 by coupling Me2PCH2Li and Me2AlCl... 

Figure 3 31P and "B NMR data for the methylene-bridged phosphine-boranes 3a-c. 

There is practically no difference in the polydispersity between PMMA samples prepared in the presence of the diamagnetic (18-electron) and paramagnetic (17-electron) closo complexes 4 and 5, respectively. On the contrary, steric factors have a quite noticeable effect on the chain propagation step and the macromolecular characteristics of the samples. Thus, if the phosphine groups at the metal center are linked via methylene bridges (complexes 4 and 5), favorable steric conditions for controlling the polymer chain growth probably occur that lead to the formation of polymers with MWDs much narrow than in the case of complex 2. 

Imamoto T, Tamura K, Ogura T, Ikematsu Y, Mayama D, Sugiya M (2010) Improved synthetic routes to methylene-bridged F-chirai diphosphine ligands via secondary phosphine-boranes. Tetrahedron Asymmetry 21 1522-1528... 

Mezzetti and co-workers, in their exploration of phosphines bearing highly symmetric and bulky substituents, used (5)-chloromethylphenylphosphine borane (Scheme 4.26) to prepare a rare example of non-C2 symmetric methylene-bridged P-stereogenic diphosphine borane. 

Compound (17) is synthesized by the treatment of the appropriate cyclic amine with tris(dimethylamino)phosphine at 100 °C, resulting in the elimination of three moles of dimethylamine. The products obtained are dependent on the number of methylene groups bridging the nitrogen atoms. When all four bridges are ethylene, (CH2)2, only (17a) is observed when all are trimethylene, (CH2)s, only (17b) is found. When there are two of each type, both tautomers are present. 

While much of the efforts in osmium cluster chemistry are on synthesis and structural characterization, there have been a number of important studies on reactions in solution, particularly on isomerization reactions. The reaction between diazomethane and Os3(/u,-H)2(CO)io produces a mixture of a methyl complex Os3(/x-H)(CH3)(CO)io and a methylene complex Os3(/U.-H)2(/U.-CH2)(CO)iq. Variable-temperature NMR studies showed that these two isomers are in equilibrium and that the methyl group interacts with a second osmium center through a C-H-Os bridge. Two isomers of the substituted vinyl compound Os3(CO)gL(/U.-H) (/x-CH=CH2) are in equilibrium in solution. The position of the equilibrium depends on the size of the phosphine ligand, L. There is a similar steric effect in the equilibration of methyl and methylene tautomers of Os3(/u.-H)2(/U.-CH2)(CO)gL and Os3(/u.-H)(CH3)(CO)gL with larger ligands favoring the methylene complex. 

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