SYNTHESIS AND CHARACTERIZATION OF 4-COORDINATE AND 5-COORDINATE ORGANOALUMINUM COMPLEXES INCORPORATING THE AMIDO DIPHOSPHINE LIGAND SYSTEM N(SIME(2)CH(2)PPR(2)(I))(2)

The preparation of new four- and live-coordinate aluminum amido diphos phine complexes is reported. The reaction of the potentially tridentat e ligand precursor LiN(SiMe(2)CH(2)PPr(2)(i))(2) with AlCl3 in toluene at 25 degrees C leads to the formation of AlCl2[N(SiMe(2)CH(2)PPr(2)( i))(2)]. The X-ray crystal structure shows it to be monomeric with a d istorted-trigonal-bipyramidal geometry having the tridentate ligand me ridionally bound. The solution NMR spectra are also consistent with th is geometry. Addition of the alkyllithium reagents RLi (where R = Me, Et) or dialkyl magnesium reagents R(2)Mg (R = Me, CH(2)Ph) leads to th e formation of bis-(hydrocarbyl) derivatives of the formula AlR(2)[N(S iMe(2)CH(2)PPr(2)(i))(2)]. The X-ray structure of Al(CH(2)Ph)(2)[N(SiM e(2)CH(2)PPr(2)(i))(2)] shows that it is mononuclear in the solid stat e with a distorted-tetrahedral geometry in which coordination to only one phosphine is observed. Variable-temperature NMR studies are consis tent with a rapidly fluxional molecule at ambient temperature. In solu tion, the NMR spectroscopic parameters of AlMe(2)[N(SiMe(2)CH(2)PPri(2 ))(2)] and AlEt(2)[N(SiMe(2)CH(2)PPr(2)(i))(2)] are consistent with ov erall C-2 upsilon symmetry. These observations are supported by Al-27 NMR studies. Attempts to generate the monoalkyls Al(R)X[N(SiMe(2)CH(2) PPri(2))(2)] (R = Me, Et; X = Cl) by the addition of 1 equiv of the ap propriate alkylating reagent results in equimolar mixtures of the corr esponding dialkyl and dichloride; however, the reaction of the lithium salt LiN(SiMe(2)CH(2)PPr(2)(i))(2) with RA1Cl(2) (R = Me, Et) produce s mixtures containing predominantly Al(R)X[N(SiMe(2)CH(2)PPr(2)(i))(2) ] (R = Me, Et). Treatment of the monoethyl derivative with excess AlCl 3 affords AlCl2[N(SiMe(2)CH(2)PPr(2)(i))2]. AlCl3. The X-ray crystal s tructure of this compound shows it to be monomeric, with each phosphin e bound to a tetrahedral Al center. Solution NMR studies are consisten t with this geometry. This species is likely formed as the result of t he coordination of an AlCl3 molecule to the aluminum center, followed by coordination of a second molecule to a free phosphine and subsequen t elimination of EtAlCl(2). This species is also generated by the addi tion of 3 equiv AlCl3 to the starting lithium salt LiN(SiMe(2)CH(2)PPr (2)(i))(2).