Cyclic arsines structure

The cyclic arsine (AsMe) reacts with Mn2(CO)jQ at room temperature in daylight to give [Mn2(CO)g(AsMe)5] and at high temperature to give [MnlCOlj-(AsMe) ]2 structures (5) and (6) are proposed in which the metal-metal bond is replaced by bridging arsenic atoms. The crystal structure of [( 0)5-MnAsMc2Cr(CO)5] has been reported. The arsenic atom bridges the two... 

A masked allylic boron unit can be revealed through a transition-metal-catalyzed borylation reaction. For example, a one-pot borylation/allylation tandem process based on the borylation of various ketone-containing allylic acetates has been developed. The intramolecular allylboration step is very slow in DMSO, which is the usual solvent for these borylations of allylic acetates (see Eq. 33). The use of a non-coordinating solvent like toluene is more suitable for the overall process provided that an arsine or phosphine ligand is added to stabilize the active Pd(0) species during the borylation reaction. With cyclic ketones such as 136, the intramolecular allylation provides cis-fused bicyclic products in agreement with the involvement of the usual chairlike transition structure, 137 (Eq. 102). 

Ligands such as phosphines (PRj) and arsines (AsRs) (R = alkyl, aryl, halogen, etc.) form complexes with a variety of metals in various oxidation states. Vibrational spectroscopy has been used extensively to determine the structures of these compounds and to discuss the nature of the metal-phosphorus (M-P) bonding. Verkade reviewed spectroscopic studies of M-P bonding with emphasis on cyclic phosphine ligands. 

Recently, the structure and chemistry of materials of the type (SiH2) and (SiH) have been investigated and reviewed. However, these compounds cannot be considered analogous to the alkene or alkyne series in carbon chemistry because of their polymeric nature. The inability of silicon to form multiple bonds with itself or other elements is well known, but perhaps not easily explained. It might be pointed out that none of the elements below the second period in the periodic table appears to form stable double bonds with themselves. For example, the compounds phosphobenzene and arsenobenzene, supposedly analogs of azobenzene, are better described as tetraphenylcyclotetraphosphine and hexaphenylcyclohexa-arsine, respectively. Also, sulfur, under ordinary conditions, exists as a cyclic octamer. 

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