Alternatives for Cyclopentadienyl Ligands in Organoyttrium Chemistry:  Bis(N,O-bis(tert-butyl)(alkoxydimethylsilyl)amido)yttrium Compounds

Abstract

Reaction of YCl3·THF3.5 with 2 equiv of [Me2Si(NCMe3)(OCMe3)]Li produces [Me2Si(NCMe3)(OCMe3)]2Y(μ-Cl)2Li·THF2 (1), which easily loses LiCl to give [Me2Si(NCMe3)(OMe3)]2YCl·THF (2). Salt metathesis of 2 with LiBH4, LiOAr (OAr = O-2,6-(CMe3)2C6H3), NaN(SiMe3)2, and LiCH(SiMe3)2 gives the corresponding yttrium bis((alkoxysilyl)amido) derivatives, [Me2Si(NCMe3)(OCMe3)]2YR (R = BH4·THF (3), OAr (4), N(SiMe3)2 (5), CH(SiMe3)2 (6)). The alkyl compound 6 reacts with H2 in THF to give an unstable hydride {[Me2Si(NCMe3)(OCMe3)]2Y(μ-H)}2 (7), which was identified by 1H NMR as a symmetric dimer in solution. Isolation of the hydride 7 appeared not to be possible; the disproportionation product, [Me2Si(NCMe3)(OCMe3)]3Y (8), was obtained instead. With HC≡CR, 6 undergoes protolysis of both the alkyl and the (alkoxysilyl)amido ligands to yield {Y(μ-C≡CR)3} n for R = SiMe3 (9) and CMe3 (10). In contrast, polymerization to polyphenylacetylene was observed for R = Ph. Compound 6 reacts with N≡CMe with metalation of the methyl group under proton transfer to the alkyl ligand to give CH2(SiMe3)2. Insertion of another N≡CMe into the new Y−C bond and 1,3-H shift produces {[Me2Si(NCMe3)(OCMe3)]2Y(μ(N,N‘)-NHCMeCHC≡N)}2 (11). The molecular structures of 6 and 11 show that the bis(N,O-bis(tert-butyl)(alkoxydimethylsilyl)amido) ligand system is slightly more bulky than the bis(pentamethylcyclopentadienyl) ligand set in compounds Cp*2YR. A ROHF INDO/1 semiempirical molecular orbital study on a stripped and symmetrized model of 6, [H2Si(NH)(OH)]2YCH3, shows that the electronic properties of the bis((alkoxysilyl)amido) ligand system are quite different from those of [C5H5]2YCH3 but compare well with those of the bis(benzamidinato) analogue [HC(NH)2]2YCH3. The (alkoxysilyl)amido ligand binds dominantly through a strong, ionic Y−N bond, while the ether function coordinates only weakly. Like in the bis(benzamidinato)yttrium system, the (alkoxysilyl)amido and the alkyl ligands accumulate negative charge, resulting in essentially ionic compounds. This high ionicity makes the compounds have little tendency to engage in σ-bond metathesis reactions and (catalytic) insertion chemistry. Because of the absence of charge delocalization within the (alkoxysilyl)amido ligands, these behave as strong Brønsted bases and compete successfully with the Y−C bond in C−H bond activation reactions.

Addition of Nitriles to Alkaline Earth Metal Complexes of 1,2‐Bis[(phenyl)imino]acenaphthenes

“…The product of this reaction, [Y{Me 2 Si(NCMe 3 )OCMe 3 )} 2 -{N(H)C(CH 3 )C(H)CN}(thf)] 2 is a dimer that consists of two crotonitrileamido ligands bridging two yttrium atoms, as shown by single-crystal X-ray diffraction. [10] The reaction of [Re(CO) 3 (bpy)(NCCH 3 )]OTf with sodium hydride in THF proceeds with nucleophilic attack at the nitrile group coordinated to the rhenium(i) center and produces a dinuclear complex in which one bridging crotonitrileamido ligand connects the Re atoms. [11] The keteniminate [Ir(Cp*)(Me 3 P)Ph-(N=C=CPh 2 )] [12] was prepared by treatment of [Ir(Cp*)-(Me 3 P)Ph(OH)] with diphenylacetonitrile and catalytic amount of [Ir(Cp*)(Me 3 P)Ph(OTf)].…”

Modular N,O‐Chelating Ligands: Group‐4 Amidate Complexes for Catalytic Hydroamination

“…[2,3] Examples of these classes of ligands have included, but are not restricted to, amidinates, [4][5][6][7][8] troponiminates, [9,10] guanidinates, [11][12][13] sulfonamides, [14,15] nitrogen-based ligands [16][17][18] and chelating nitrogen and oxygen ligand sets. [19][20][21] In surveying the literature, it became apparent that while many [ elaborate ligand classes have been studied, a very simple group of N,O-chelating molecules, namely deprotonated organic amides (amidates), has been largely overlooked. Amides are readily synthesized and the starting materials are widely available.…”

Solvent-Free Lanthanoid Complexes Derived From Chelation-Supported Organoamide Ligands

“…However, in comparison to the stability offered by the cyclopentadienyl ligand in [Ln(Cp) 2 (X)] (X ϭ anion), the labile nature of organoamide ligands in such systems has often caused ligand redistribution, resulting in the isolation of homoleptic derivatives. [7,15,22,25,26] The incorporation of a supporting donor atom to give a bidentate amide ligand may improve the stability of the heteroleptic complexes. Encouragement for this idea came from the observation that N,N-dimethyl-NЈ-trimethylsilylethane-1,2-diaminate (enЈ) gave not only the homoleptic complexes [Ln(enЈ) 3 ] (Ln ϭ Lu, Er, Eu, Sm, Nd, La) but also a single example of a heteroleptic derivative [Er(enЈ) 2 Cl].…”