7-Phosphanorbornadiene complexes

Treatment of the corresponding iV-methyl(benzylidene)amine with excess of 7-phosphanorbornadiene complex 137 afforded 1,2,3-azadiphosphetidine 35 as the major product (Scheme 51) <1998HAC597>. The proposed reaction mechanism included the generation of a transient phosphinidene complex and formation of the unstable intermediate azaphosphiridine 138. Insertion of the second molecule of phosphinidene into the weak P-N bond of the three-membered heterocycle 138 afforded the 1,2,3-azadiphosphetidine 35. 

The thermolysis of 7-phosphanorbornadiene complex 56a (R = Me) in toluene at 110°C in the presence of 1,3,5-triphosphinine P3C3Bu 3 led to a 1 8 equilibrium mixture of the tetraphosphanorbornadiene complex 57a and the tetraphosphaquadricyclane derivative 58a. Fractional crystallization from a hexane-dichloromethane solution furnished yellow crystalline 58a (49% yield) and orange crystalline 57a (6% yield) (Scheme 21). 

The phosphirene compound was prepared from the 7-phosphanorbornadiene complex as shown in Scheme 22.2 8 The complex converts to 2-keto-l,2-dihydrophosphete complex by insertion of CO into P—C bond via metallacycle intermediates.299 Analogous phosphirene,300 phosphirane,301 and the related alkenylidenephosphirane293 derivatives have been reported. 

Finally, we draw this section to a close by mentioning nitrilium phosphine ylide complex (164), which is perhaps more accurately described as a low-valent organophosphorus species (see Chapter 1) rather than a conventional ylide. Complex (164) has been identified as an intermediate in the thermally induced conversion of 7-phosphanorbornadiene complexes into 2H-l,2-azaphosphole complexes (Scheme 34). ... 

So far, only very few reactions were reported on the use of 2H-azaphosphirene complex 11a in nitrilium phosphanylid complex chemistry, mainly because of the tendency of P-CjMes-substituted derivatives to undergo side reactions [47]. Nevertheless, it seems worthwhile to look at the reaction of 11a with DMAD, which finally led to the 1 -aza-7-phosphanorbornadiene complex 13 via 2H-l,2-azaphosphole complex 12 as reactive intermediate (Scheme 9) [48]. Later on, complex 12 was isolated and characterized using a different stoichiometry [49]. 

Scheme 9. Synthesis of l-aza-7-phosphanorbornadiene complex 13 via 2H-l,2-azaphosphole complex 12 [48]...

A real landmark in the generation of transient nitrilium phosphanylid complexes was the discovery that 7-phosphanorbornadiene complexes could be also employed, e.g., the complexes 14a,b in the synthesis of 2H-l,2-azaphosphole complexes 16a,b (Scheme 10), thus offering now the possibility to study the reactivity of sterically less encumbered 1,3-dipole species such as 15a,b [34]. Note worthy is the absence of any by-products such as A -l,3,2-oxazaphospho-lene complexes (cf. Scheme 7) in these reactions. Even more fascinating are perspectives to use 7-phosphanorbornadiene complexes with P-functional substituents in 2H-l,2-azaphosphole complex chemistry. 

Meanwhile, 7-phosphanorbornadiene complexes can be also employed in the synthesis of 2H-l,3,2-diazaphosphole complexes although, in such cases competing reactions were observed, leading also to 2H-l,4,2-diazaphosphole complexes [52]. 

Besides furan, the Diels-Alder reaction between other heteroaromatics and arynes is also known. The [A+2] cycloaddition of benzyne with 3,4-dimethylphos-phole pentacarbonylmolybdenum complexes 133 has recently been reported by Mathey (Equation 12.37) [75]. The cycloaddition mainly takes place on the less-hindered side of the phosphole ring, affording 2,3-benzo-7-phosphanorbornadiene complexes 134 in moderate yields. 

Prepare a pressure-Schlenk tube (100 mL) according to step 1. Charge the tube with the phosphanorbornadiene complex 5 (4.80 g, 6.24 mmol), toluene (40 mL) and a threefold excess of diphenylacetylene (2.02 g, 19 mmol). 

Finally, the phosphinidene complex 40, as generated from the appropriate 1-phosphanorbornadiene complex 39, readily rearranges to give the l-chloro-2-vinylphosphirane complex 41 and its formal dimer 42 (Scheme 16) <20050M2930>. 

The most widely employed electrophilic phosphinidene complexes are generated from M(C0)5 (M=W, Mo, Cr) complexed 7-phosphanorbornadienes 7, which were reported by Marinetti et al. in 1982 [46]. They trapped the transient phosphinidene complex 8 at 110 °C (or at 55 °C if CuCl was used as catalyst) with olefins and alkynes to obtain three-membered phosphiranes and phosphirenes, respectively. 

Cheletropic elimination of the in situ generated phosphinidene complex 8 from the 7-phosphanorbornadiene precursor is believed to be the rate-determining step before 1,2-cycloaddition occurs to the unsaturated hydrocarbon. Without catalysts these are first-order processes that depend only on the concentration of the precursor and not on that of any substrate [47]. The configu-... 

If VOCl3(DME) is used, the cyclization of P-alkyne 44a leads to a mixture of isomers of tetrachloro-1 A3,2A3-diphos-phetane 99 (Scheme 32) <2003ZNB44>. A twofold W(CO)s-complexed 1 A3,2A3-diphosphetane was obtained as a side product in low yield from a specifically substituted (phosphanorbornadiene)W(CO)s complex in the presence of CuCl <20050M2930>. 

A T-WICOls complex of a 1-unsubstituted lf/-l,2-azaphosphole was assumed to be an intermediate in the [3-F2] cycloaddition of a nitrilium phosphane ylide P-W(CO)s complex, with dimethyl acetylenedicarboxylate. It reacts further with another equivalent of dimethyl acetylenedicarboxylate to give a 7-aza-l-phosphanorbornadiene as the final product <1999AGE215>. 

This reaction permitted the successful construction of a stable 7-phosphanorbornadiene derivative. While it was not possible to release the free phosphine from the complex, the complexes acted, on thermolysis, as precursors of the synthetically valuable phosphinidene complex, RPM(CO)s. 

Decomposition of 7-phosphanorbornadiene using CuCl can be affected with azulene the so-formed phosphinidine complex [PhPW(CO)5] can either insert into a C-H bond on the five-membered ring or form a 1,4-adduct with the seven-membered ring (eq 39)." ... 

---