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Donor atom substitutions in amidophosphine ligands : early transition metal complexes of arsine and aryloxide containing ligands Carmichael, Christopher David

Abstract

The effects of donor atom substitution in the amidophosphine ligands [sup PH][P₂N₂] (where [sup PH][P₂N₂] = PhP(CH₂SiMe₂NSiMe₂CH₂) ₂PPh) and [sup PH][NPN] (where [NPN] = PhP(CH₂SiMe₂NPh) ₂ with both stronger and weaker donors is explored through early transition metal coordination chemistry. The diamidodiarsine macrocycle Ph[As₂N₂] (where [sup PH][As₂N2₂] = [sup PH]As(CH₂SiMe₂NSiMe₂CH₂)₂AsPh) can be synthesized as a 1,4-dioxane adduct of the dilithium salt, [sup PH][As₂N₂]Li₂ ( 1,4-dioxane). Reactions of the lithium salt with appropriate metal halides affords the complexes [sup PH][As₂N₂]ZrCl₂ ,[sup PH][As₂N₂]TiCl₂ and ([sup PH][As₂N₂]Y) ₂ (μ-Cl) ₂, The yttrium complex is the first structurally characterized complex containing an yttrium arsenic bond. Attempts to reduce the halide salts in the presence of dinitrogen lead to mixtures of products, and evidence points to the reduction of arsenic within the macrocycle. The chelating diamidoarsine [sup PH] [NAsN] (where [sup PH] [NAsN] = PhAs(CH₂SiMe₂NPh)₂) can be synthesized as a THF adduct of the lithium salt, [sup PH] [NAsN]Li₂ (THF)₂ . Reaction of the lithium salt with TaMe₃Cl₂ affords the fivecoordinate alkyl complex [sup PH][NAsN]TaMe₃ . Hydrogenation of [sup PH] [NAsN]TaMe₃ does not produce a hydride complex, but instead a modest yield of the protonated ligand precursor [sup PH] [NAsN]H₂. Evidence suggests that [sup PH] [NAsN]H₂ is produced through hydrogenation of tantalum-amide bonds. Density functional theory calculations carried out on the model complexes 'NAsN'TaMe₃ and ('NAsN'Ta)₂ (μ-H)4 (where 'NAsN' CH₃As(CH₂SiH₂NCH₃)₂ ) suggest that dissociation of the arsenic donor may play a role in the hydrogenation of the trimethyl complex. The bis(aryloxy)phosphine ligands R[OPO] (where [sup R][OPO] = RP(3,5- (Bu₂C₆H₂0 ) ₂) (R = Ph, 'Pr) are prepared as dimeric lithium salts ([sup R][OPO]Li₂)₂ (THF)₄, protonated ligand precursors R[OPO]H₂ , the dimeric potassium salt ([sup PH] [OPO]K₂)₂ (THF)₆, and trimeric ([sup Pr][OPO]K₂)₃(THF)₃ . Reaction of [OPO] precursors with group 4 and 5 halides affords [sup PH][OPO]MCl₂ (THF) (M = Ti, Zr, Hi) and R[OPO]TaCl₃ . Direct alkylations of [sup PH][OPO]TaCl₃ produce only mixtures of products; however, the methyl complexes [sup PH][OPO]TaMeC₂ , [sup PH][OPO]TaMe₂Cl and [sup PH][OPO]TaMe₃ can be prepared by reaction of [sup PH][OPO] precursors with TaMe₃Cl₂. Alkylation and reduction chemistry of the halide complexes is dominated by the formation of bis-ligand complexes, including [sup PH][OPO]₂Ti, likely a result of the reduced steric bulk that is inherent to these metal-ligand systems. Preliminary investigations suggest it may be possible to prepare dinitrogen complexes through reactions with hydrazine and substituted hydrazines, or through ligand exchange with the dinitrogen complex [TaCl₃(THF)₂] ₂ (μ-N₂).

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