Phosphaalkenes carbonyls

A number of benzo- or dibenzo-fused seven membered phosphorus heterocyclic systems have also been studied. These include the benzo-fused oxa-bridged phosphaalkene 76 prepared by thermolysis of 2,3-diphenylindenone 23-epoxide (as a source of the carbonyl ylide 1,3-dipole intermediate) in the presence of /-butylphosphaalkyne. This bridged phosphaalkene is unusually stable even without inert gas blanketing . Reaction of 76 with sulfur or grey selenium stereoselectively affords the thia- or selenaphosphiranes 77 (X = S, Se respectively). <00T6259>... 

Complexation of phosphorus-containing multiple-bond systems to transition metals has been investigated extensively in recent years. In this regard, bonding between the phosphaalkene and transition metal carbonyls can be achieved via the free electron pair of the phosphorus (tjl coordination, type A) (149-151) as well as via the n system (r 2 coordination, type B) (152-154). The latter reaction type can be explained by two different electronic resonance structures. Type C is a combination of the two possibilities and can be occasionally observed (155, 156) (Fig. 23). 

Various bicyclic phosphaalkenes 21-24 were synthesized from oxirane 118. Acceptor-substituted oxiranes underwent a ring opening under thermal stress to give the unstable carbonyl ylides. It was shown that upon heating 2,3-diphenylindenone oxide 118 underwent conversion into ylide 119, which can react with various phosphaalkynes in [3+2] cycloaddition reaction to give 21-24 <2000T6259>. 

The scope and limitations of the base-catalysed Phospha-Peterson synthesis of phosphaalkenes of the type MesP=CRR (R,R = aryl), involving the reaction of MesP(SiMc3)2 and a carbonyl compound in the presence of a trace of KOH or NaOH, has been investigated and shown to provide a convenient and general route to these compounds in 40-70% yield, usually as a 1 1 mixture of E- and Z-isomers. A simple access to a series of l,l -ferrocenylenebis(dihalophosphines) has facilitated the synthesis of the first metaUocene-bridged bis(phosphaalkene)... 

A new route to phosphaalkenes is provided by treatment of dichloro-phenylphosphine with two equivalents of carbonyl-functional carbenes, resulting in a two-electron reduction of the phosphorus centre coupled with carbene oxidation. A range of amido-functional phosphaalkenes, e.g., (112), (alternatively viewed as carbene-phosphinidene adducts), was prepared using this approach, followed by full spectroscopic and structural characterisation. A related diamino-functional phosphaalkene has also been described and its coordination chemistry studied. Among other new phosphaalkene systems reported is a series of phosphaalkene-phospholes, e.g., (113), the monoanionic phos-phaalkenyl-phosphido ligand (114), alkali metal salts of the phosphaalkene radical anion (115), ° and new 1,3-diphosphacyclobutadiene... 

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