1.3.4- Triphosphole complexes

A 1,3,4-triphosphole complex is prepared in the thermally induced regi-ospecific insertion of (t-Pr)(Me3Si)N-C = P into the phosphorus-phosphorus bond of species 108 to yield 109 (01AGE2471). 

Both these schemes are involved in (8.306a). Triphosphinine complexes are also known (8.306b) as well as diphosphete (8.306c) [4,5] and triphosphole complexes (8.306d,e) [6]. 

VII. Complexes of Di- and Triphospholes and Corresponding Phosphorus-Antimony Ligands... 

Figure 4. B3LYP/LANL1DZ structure of the Cr(CO)3 complex of 1,2,4-triphosphole.

In the last complex of Table 6, however, the metal atom deviates from the plane of the ring and the arrangement about P-1 is pyramidal with a sum of angles equal to 348°. This situation is described by bonding mode (2) <89NJC353>. It also applies to the 1-alkyl triphosphole with a sum of angles around P-1 of 342° <95CCl6ll>. 

By contrast, alkylation of the 1,2,4-triphospholide ion by bis(trimethylsilyl)bromomethane takes place at P-1 and affords a stable 1,2,4-triphosphole (192) which is isolated as orange crystals <95CC1661>. It gives a t-PtCl2PEt3 complex in which the triphosphole is attached via P-4 (molecular structures of the triphosphole and its complex in Table 6). By reaction with methyl iodide the triphosphole is converted to a homopentaprismane-structured phosphonium iodide (193) <94CCRl >. 

As has been mentioned in Section 4.22.12.1.1, the only known IFf-1,2,4-triphosphole forms an f/ -complex by P-4 coordination. 

Other metal substituents such as Hg [173] further decrease the barrier, and in the case of Cu both if- and if-complexation of the triphosphole could be observed [174], Apparently the low barrier is related to the stability of the transition structure, whereby the ring is highly anionic and exhibits aromaticity [5] (see also below). 

An X-ray structure determination Cmcm i i= 0.061 of pale yellow crystals of compound B obtained from the sulfur dioxide reaction, shows a neutral complex of symmetry mm2 to be present in the solid. The anionic part of the molecule consists of two anellated l,2-dihydro-5-oxo-l,2,4-triphosphol-3-olate rings which share the central P-P group (P-P 215.3 P-C 189.1 P-C 178.4 C-O 123.9pm C-P-P 98.4° C-P-C 91.2° C P C 98.7°). The lithium cations are coordinated square pyramidally (Li-0 193.5 to 209.1 pm), each binding a 1,2-dimethoxyethane and a tetrahydrofiiran ligand in addition [30]. 

The first 1,3,4-triphosphole 172 was produced by the thermally induced regiospecific insertion of phosphaalkyne P=C-N(Pr )TMS into the P-P bond of the l//-diphosphirene complex 130 (35% yield). Interestingly, a similar ring expansion was not observed with the sterically more bulky diphosphirene complex 87d, which is the precursor of 130... 

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