Studies on Sterically Protected Multiple Bonding Involving Low Coordinated Phosphorus Atoms

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Sterically protected phosphorus containing unusual compounds in low coordination states were prepared by utilizing the 2,4,6-tri-t-butylphenyl moiety (here abbreviated to the Ar group) as a protective group. Such unusual organophosphorus compounds as diphosphene (-P=P-), 1,3-diphosphaallene (-P=C=P-), and phosphaalkyne (-C*P) having low coordinated phosphorus atom(s) of coordination number 2 or 1 were isolated and characterized as kinetically stable compounds.Protective groups other than the Ar group have been developed to utilize the stabilization of low coordinated organophosphorus compounds as follows. Attempts to prepare diphosphenes involving 2,6-di-t-butylphenyl, 2,4,6-tri-t-pentylphenyl, 1,2,3,4,5,6,7,8-octahydro-1,1,4,4,5,5,8,8-octamethyl-9-anthryl, and 2,4-di-t-butyl-6-dimethylaminophenyl were successful. Strong electron-withdrawing groups, such as 2,4,6-tris(trifluoromethyl)phenyl and 2,6-bis(trifluoromethyl)phenyl, were also useful as a protective auxiliary of diphosphenes as well as unsymmetrical diphosphenes.A preparative method of 1,3-diphosphaallenes has been developed involving addition reaction of dichlorocarbene to diphosphenes leading to dichlorodiphosphiranes, which were further converted to diphosphaallenes with an appropriate alkyllithium reagent. This preparative method has been successful in preparation of some unsymmetrical diphosphaallenes' starting from unsymmetrical diphosphenes. Attempted preparations of the extended phosphacumulenes such as phosphabutatriene (-P=C=C=C ) and diphosphabutatriene (-P=C=C=P-) have been successful by this method.A new preparative method of phosphaalkynes has been developed involving elimination and intramolecular rearrangement of 1-chloro-2-phosphaethenyllithiums and the ^<31>P NMR studies have been made in an attempt to observe intermediacy of phosphorus analogue of isonitrile during this unusual rearrangement reaction.