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Methods (73)Organophosphorus compounds have been applied in two ways in chemical synthesis. They can either be used as a reagent in a step of the synthesis (for example, in the Wittig reaction) or they can be incorporated directly into the target molecule. This second application, in particular, has expanded greatly in the last few years with the preparation of low-coordination phosphorus compounds. These include the phosphaalkynes, which are of great interest to organic and inorganic chemists. Phosphaalkynes have been employed in the synthesis of heterocyclic compounds, phosphaarenes and their valence isomers, and polycyclic compounds. Further applications have been the use of phosphaalkynes as new ligand systems in complex chemistry and their cyclooligomerization with organometallic reagents. While the chemical properties of phosphaalkynes have little in common with those of nitriles, they are in many ways very similar to those of the isoelectronic acetylenes.

Dcdic,uted to ProfiJssor MorIjrcd Regit: on ihi, o i n r s i o t i qf'kis 60th birtlidu,rThe rcccntly described synthesis of the 1,3.5,7-tetraphosphabarrelene complex 3 from rerr-butylphosphaacetylene 1 and bis-(cyc1ooctatetraene)zirconium [Zr(~ot),]"~ led to the assumption that the 12-valence electron fragment [cotM], formed as an intermediate by elimination of one of the two cot ligands, is an ideal tetnplatc for cyclooligomerizations of phosphaalkynes. Phosphaalkynes are known to cyclodimerize on the 14-valence electron fragments [Cp,M'] (M = Zr, Hf) to give the 1,3diphosphabicyclo[l .l .O]butanediyl metallocenes such as 2.l" for a further 0.5 h at about 140 C and then the solvent was removed at 0.5 mhar. The resulting brown solid was suspended in pentane (20 mL). filtered with a D3 frit. uashcd with pentme. and dricd at mhar. Recrystallization from tolucne afforded 6 a (1.83 g. 6 8 % ) as brown microcrystals: m.p. 163°C (decomp.). 8a: l(3.4 g, 34 mmol) was added dropwise to a solution of 5 a (4.0 g. 11.2 mmol) in toluene (1 0 mL) and pentane (10 mL) at -78 'T and stirred for 18 h at -78 C. The green-bro*n suspension was filtered at -78 C and the residue \lashed twice with pentaiie (2 x 20 mL). Recrystallization from THF (10 mL) aFforded 8 a (5.39 g.8 3 % ) as green inicrocr)stals: m.p. ca. 138 C (dccomp.). 9 h . I (1.3 g. 13 mmol) was added dropwisc to a solution of 5b (2 08 8.4.32 inmol) in Et,O (30 mLj at 0 ' C . After 1 h the reaction solution was cooled to -~3 0 C, the green crystals o f 9 h which precipitated &'ere filtered off and dried at l o -" mhiir; 9 b(2.8 g. X9%j; n1.p. 107 C (decomp.).13: Hexachloroethane (0.2 g, 0.X6 mmol) was added to a suspension of X a (0.5 g.0.86 mmol) in toluene (30 mL) at -~ 78 C. The reaction mixture was allowed to warm to room temperature over the course of 12 h. tiltci-ed. and the tiltrate was evaporated to dryness at 0.5 mhar. The residue has dissolved in pentme (20 m L ) nnd small amounts of insoluble material were removed by liltration. The yellow filtrate wiis concentrated to 5 mL and cooled t o -78 C. After 8 h. 0.14g of 13 (53%) had precipitated in the form of ii ycllow solid; m.p. X8 C (decomp.). 14. Hcxachloroethane (425 mg. 1.8 mmolj was added to a solution of 9b (1 3 g, 1.8 mmol) in toluene (10 mL) ;it room temperature end the mixture was stirred l'or 2 h. The solvent was removed at 0.5 mbar. the residue was taken up in pentnnc (40 mL) and filtered over Cclite to remove insoluhle material On cooling to -30 C small amounts of [his(triniethylsilyl)eyclooet~tetracne]h~ifniuin dichloride precipitated. which w a s likewise filtered off. The clear filtrutc was concentrated t o 20 mL. and subsequent cooling to -30 C led to the precipitation ol' 14 (3x0 nig. 70%) in the form of orange microcrystnls: m.p. about 128 C (decomp.).

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