Heteroallenes, reaction with

The synthesis of ylides which are a-substitued with a derivative of the caiboxy group can also be achieved via the addition of simple ylides to heteroallenes. The reaction with carbon oxysulfide gives rise to the formation of betaines from which alkylthiocarbonylalkylidenephosphoranes may be generated by alkylation and subsequent deprotonation (equation 78 X = O, Y = S). Carbon disulfrde reacts in a similar way yielding (alkylthio)thiocarbonyl-substituted ylides (equation 78 X = S, Y = S). These compounds are also available from the reaction of simple ylides with trithiocarbonates or dithiochloro-carbonates in analogy to the acylation of ylides (see equations 71 and 72). ... 

The reactions with sulfur or selenium result in the formation of betaines, which can be alkylated to give semi-ylide salts (equation 98). The reactions of hexaphenylcarbodiphosphorane with a series of heteroallenes also lead to betaines which on thermolysis yield new cumulated ylides (equation 99, cf. equation 120). 

Analogous heterobimetallic tripodal amido complexes 1275 (M = Fe, Ru) undergo highly selective reactions with heteroallenes X=C=Y (C02, CS2, OGNPh, SCNMe, SCNPh) to yield the insertion products 1276 (Equation (65)).962 Single crystal X-ray structures of the products (1276 M = Fe X = Y = S X = S, Y = NPh) established the mode of coordination of the substrates to the two metal centers as depicted in Equation (65). The Zr-Fe complex CpFe(CO)2Zr(OBut)Cp2 reacts with 1 equiv. of CS2 to form the analogous stable dithiocarboxylate complex.963... 

C3-symmetrical tripodal ligands have been used to obtain amido complexes of family (86). If chiral substituents are present in the ligand periphery, some stereo discrimination is observed in the reaction with several chiral ketones and aldehydes. On the other hand, such systems can generate early-late heterobimetallics with metal-metal bonds (equation 41). Reaction of (91) with MeNC as well as the heteroallenes CO2, CS2, RNCO and RNCS led to insertion into the polar metal-metal bond. Tris (pyrazolyl) borate see Tris(pyrazolyI)borates) Zr and Hf complexes are other interesting examples of the type (86). In combination with MAO, they give promising results in ethylene and ethylene/hexene polymerizations. Substitution of these sterically crowded ligands allows adjustements of the environment of the active site to the... 

Lithium phosphanylidene carbenoid 1 is a starting material for synthesis of heavy heteroallenes such as -P=C=E (E=Si<, Ge<, P-, As-) [51]. Lithium carbenoid la was allowed to react with diarylsilyl dichloride 47 to afford the corresponding adduct 48, which gave 1,3-phosphasilaallene 49 on the reaction with t-butyllithium. Phosphasilaallene 49 is observed below 0°C in the P-NMR... 

Scheme 1 gives a postulated reaction pathway for all these metathesis like reactions. The heteroallenes or the heteroalkenes are supposed to react in a 2 + 2 cycloaddition reaction with Cl3(dme)WCtBu to form metalla cyclobutene derivatives. Electrocyclic ringopening reactions of these (not isolated) metallacycles yield tungsten imido or 0X0 complexes with sigma bonded vinyl, iminyl, ketenyl or keteniminyl ligands. 

Scheme 4.7 Insertion and fragmentation of heteroallenes upon reaction with the Zr-lr complex 16.

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