The Deprotonated Iminophosphoraneo-C6H4PPh2P=NSiMe3 as a Novel Chelating Ligand in Organocopper(I) and -zinc(II) Chemistry

Abstract

Lithiation of triphenyl(trimethylsilylimino)phosphorane Ph3P=NSiMe3 with MeLi gives the ortho‐metallated species [Li(o‐C6H4PPh2NSiMe3)]2·Et2O (1), which exhibits all the requirements of an organometallic ligand capable of side‐arm donation. The deprotonated ortho‐phenyl carbon atom gives access to metal–carbon σ bonds in transmetallation reactions, while the Ph2P=NSiMe3 moiety can donate to the same metal center through the imine nitrogen atom. In transmetallation reactions with CuBr, the dimeric organocopper complex [Cu(o‐C6H4PPh2NSiMe3)]2 (2) is obtained, while application of ZnCl2 yields the monomeric zinc complex [Zn(o‐C6H4PPh2NSiMe3)2] (3). Reaction with CuCl2 gives access to the new diiminophosphorane (o‐C6H4PPh2NSiMe3)2 (4) through oxidative coupling at the ortho positions. In all the metal complexes, the Ph2P=NSiMe3 residue acts as a side‐arm donating group through the nitrogen atom. The intermolecular N→Cu donor bond in 2 is as short as copper–amide bonds, while the N→Zn bond lengths in 3 are in the region normally found for donor bonds. Compound 4 is a molecule, possessing two Ph2P=NSiMe3 moieties bridged by a biphenylene group.

Structural Organozinc Chemistry

“…Compound 69 123 contains two C,N-chelate-bonded iminophosphorane ligands and was obtained from the reaction of ZnCl 2 with two equivalents of the corresponding ortholithiated derivative 124 . An X-ray structure determination of 69 revealed a molecular geometry as shown in Figure 36.…”

Orthomercurated and cycloaurated derivatives of the iminophosphorane Ph3PNPh

“…We have shown previously that direct cyclo-manganation and -rheniation of Ph 3 P=NPh occurs readily to give 2 [6]. (1) (2) M = Mn or Re As far as we are aware these are the only cyclometallated derivatives of iminophosphoranes involving transition metals that have been prepared directly, though other examples of both transition-and main-group metal derivatives have been synthesised via ortho-lithiation of Ph 3 P=NR' followed by coupling with appropriate metal halides [7,8].…”

C,C- and C,N-Chelated Organocopper Compounds

“…Additionally, both Zhu's and Sundholm's calculations reveal that lithium counterions play an important role in these organocopper complexes [74,75]. As shown in Scheme 11, the C,N-chelated dicopper compounds 37,38 and 40-42 documented in the literature are generally macrocyclic neutral species since the two negative ligand charges are exactly balanced with two Cu(I) atoms [76][77][78][79][80][81][82]. An early example of structurally well-defined alkylcopper compounds was [Me3SiCH2Cu]4, in which trimethylsilyl groups not only pose steric hindrance to increase the stability but also improve the solubility by virtue of the lipophilicity of the silicon groups [83,84].…”

“…However, with a smaller steric effect, the alkyl-pyridine ligands will bind four copper atoms, generating a tetracopper complex 39 [77]. Similarly, three dicopper compounds 40-42 based on 1-azaallyl, aryl-phosphanimine, and aryl-imine ligands were synthesized from the corresponding lithiated starting materials and copper salts by Lappert [78], Stalke [79], and Schmidt [82], respectively. The Cu-C bonds of 37-40 are in the range of 1.93-1.95 Å, which suggests a mostly 2c-2e Cu-C bond, while the Cu-C As shown in Scheme 11, the C,N-chelated dicopper compounds 37,38 and 40-42 documented in the literature are generally macrocyclic neutral species since the two negative ligand charges are exactly balanced with two Cu(I) atoms [76][77][78][79][80][81][82].…”