Ruppa P. Kamalesh Babu

Early transition metal and lanthanide bis(iminophosphorano)methandiide complexes; ‘pincer’ and bridging bis(phosphorus) metal carbenes

Abstract The spontaneous double deprotonation of bis(iminophosphorano)methane ligands with alkyl or bis(trimethylsilyl)amido metal precursors yields ‘pincer’ carbenes of Group 4 and lanthanide metals. The generality of the system is extended with the dilithiumbis(iminophosphorano)methandiide salt which is obtained by lithiating bis(trimethylsilylimino(diphenylphosphorano))methane with two moles of lithium alkyl. This dilithium salt reacts with metal halides with metathetical elimination of LiCl to access the same types of pincer complexes. Herein the synthesis of a complete triad of Group 4 ‘pincer’ complexes is reviewed and their reaction chemistry demonstrating (a) nucleophilic alkylation, (b) the Lewis Acidity of the metal, (c) 1,2 addition across the Mue605C carbene bond and (d) [2+2] cycloaddition across this Mue605C bond is surveyed. The structural data for the ‘pincer’ complexes suggests strongly that there is a Mue605C carbene double bond. The addition reactions also support this interpretation because a Mue5f8C bond persists after the addition. The reactivity pattern also strongly suggests that the chemistry of this carbene center is similar to the metal alkylidene complexes, and not the Fischer heteroatom carbene complexes. The chemistry extends to many other elements. The extension to Sm as a representative lanthanide is described. This species adopts a structure very similar to the Group 4 ‘pincers’. Chromium(II) gave a novel bridging carbene dimer instead of the monomeric pincer. This bridging structure is developing as another structural motif in this system.

PH2P(NSIME3)2CLI2 : A DILITHIUM DIANIONIC METHANIDE SALT WITH AN UNUSUAL LI4C2 CLUSTER STRUCTURE

Four lithium atoms in a square-planar arrangement are capped by two carbon atoms and encapsulated by NSiMe3 chelation in the dilithium methanide salt 1. This air- and moisture-sensitive complex is formed by the reaction of CH2 (Ph2 P=NSiMe3 )2 with alkyl- or aryllithium reagents.

[Ph2P(NSiMe3)]2CLi2: ein dianionisches Dilithiummethanidsalz mit einer ungewöhnlichen Li4C2-Clusterstruktur

Vier Lithiumatome in quadratisch-planarer Anordnung werden im Lithiummethanidsalz 1 von zwei Kohlenstoffatomen uberdacht und durch chelatbildende NSiMe3-Einheiten umschlossen. Dieser luft- und feuchtigkeitsempfindliche Komplex bildet sich bei der Reaktion von CH2(Ph2P = NSiMe3)2 mit Alkyl- oder Aryllithiumreagentien.

The first hafnium methandiide complexes: the assembly of an entire triad of group 4 metal ‘pincer’ bis(phosphinimine) complexes possessing the MC carbene–ylide structure

Dichlorobis[bis(trimethylsilylamido)]hafnium(IV) nreacts with n(R2PNSiMe3)2CH2 (R = nCy, Ph) cleaving the C–H bonds of the P–C–P backbone nmethylene group and eliminating 2 mol of hexamethyldisilazane to yield the nhafnium methandiide (carbene) complexes 3 and 4, thus completing the triad nof group 4 metal complexes containing the MC moiety.

Mono- and bis-(iminophosphoranyl)methane titanium complexes

The reaction of the bis(iminophosphoranyl)methanes, CH2(R2PNSiMe3)2 (Rxa0=xa0Ph 1, Me 2 or Cy 3) with two equivalents of Cp*TiCl3 (Cp*xa0=xa0C5Me5) gave, via elimination of two moles of trimethylsilyl chloride, the air and moisture sensitive bimetallic titanium bis(iminophosphoranyl)methane complexes, [(Cp*TiCl2)2{μ-(NPR2)2CH2-κN,N′}] (Rxa0=xa0Ph 7, Me 8 or Cy 9). The monometallated complexes, [Cp*TiCl2{(NPR2)CH2(R2PNSiMe3)-κN}] (Rxa0=xa0Ph 4, Me 5 or Cy 6) were observed as intermediates in the reaction by 31P NMR spectroscopy but attempts to isolate the pure monosubstituted products from reactions of the bis(silyliminophosphoranyl)methane and the titanium reagent conducted under equimolar stoichiometry were not successful; instead only mixtures of the mono- and di-substituted complexes were generated. Crystal structures of 7 and 8 revealed different molecular structures; in 7 the imidotitanium groups lie in a mutual trans orientation across the molecule whereas in 8 they lie on the same side of the molecule.