The new titanium dicarboxylate complex Cp*TiMe(OOC)2py (2) [Cp*=eta5-C5Me5; (OOC)2py = 2,6-pyridinedicarboxylate] has been synthesized. The reaction of complex 2 with water renders [Cp*Ti(OOC)2py]2O (3). The molecular structure of 3 has been studied by X-ray diffraction methods. Complex 2 reacts with isocyanides to yield the respective iminoacyl derivatives Cp*Ti(eta2-MeCNR)(OOC)2py [R=tBu (4), 2,6-dimethylphenyl (xylyl) (5)]. The molecular structure of complex4 has been established by X-ray diffraction. Compound 2 has been employed as a new building block for the preparation of new early-late heterometallic compounds; it reacts with [M(mu-OH)(COD)]2 (M = Rh, Ir) to give the corresponding tetranuclear metallomacrocycle derivatives [Cp*Ti{(OOC)(2)py}(mu-O)M(COD)]2 [M = Rh (6); Ir (7)]. The molecular structure of 6 has been established by X-ray diffraction.

The new tantalum dialkoxide complexes Cp*TaCl 2 (OCH 2 ) 2 py (1), trans-Cp*TaMe 2 (OCH 2 ) 2py (2), and cis-Cp*TaMe 2 (OCH 2 ) 2 py (3) (Cp* ) η 5 -C 5 Me 5 ; (OCH 2 ) 2 py ) 2,6-pyridinedimethoxide) have been synthesized. The molecular structures of complexes 1 and 2 have been studied by X-ray diffraction methods. The reaction of complex 3 with carbon monoxide renders Cp*Ta-(η 2 -Me 2 CO)(OCH 2 ) 2 py (4), while with isocyanides yields the respective azatantalacyclopropanes Cp*Ta(η 2 -Me 2 CNxylyl)(OCH 2 ) 2 py (6) (xylyl ) 2,6-dimethylphenyl) and Cp*Ta(η 2 -Me 2 CN t Bu)(OCH 2 ) 2 py (7). The molecular structure of complex 4 has been established by X-ray diffraction. The coordinated ketone in 4 can be reduced to 2-propanol in the presence of water. On the other hand, compound 3 reacts with triflic acid (HOTf) to render the corresponding cationic derivative [Cp * TaMe(OCH 2 ) 2 py]OTf (8).

3 and tmtaaH 2 , the macrocyclic ligand 6,8,15,17-tetramethyldibenzotetraaza[14]annulene, depending on the stoichiometry, solvent and temperature. The crystal structure of Ce(tmtaa) 2 is isostructural with Zr(tmtaa) 2 , however magnetic susceptibility measurements in the range 5-300 K show that Ce(tmtaa) 2 is not diamagnetic, but is a temperature-independent paramagnet (TIP), similar to Ce(cot) 2 , cerocene. 2 , and phthalacyanines, pcH 2 . Although all of these ligands form stable dianions, their electronic structure and therefore the electronic properties of their complexes are different. The tmtaa 2-is a 24 π-electron system (4nπ, n= 6) that is not Hückel aromatic. The negative charge is not delocalized over its entire framework, but is localized on the four nitrogen atoms, that carry a total negative charge of -0.98 e, and the two β-carbon atoms in the imidinate ring that carry a -0.24 e charge, NC α (Me)C β (H)C α (Me)N. 6,7 The tmaa 2-is therefore not planar but is saddle shaped with idealized C 2v symmetry. 8 The cot 2-(4nπ+2, n=2) and porph 2-(4nπ+2, n=6) are aromatic and the negative charge is delocalized over the planar rings. Pr, Nd, Sm, Gd, Tb, Er and Yb. 30 In this paper the synthesis and physical properties of Ce(tmtaa) 2 and related complexes are described. Results and Discussion Synthesis and StructureThe synthesis of the complexes involves the reaction of tmtaaH 2 with Ce[N(SiMe 3 ) 2 ] 3 in various molar ratios. Proton transfer reactions of Ce[N(SiMe 3 ) 2 ] 3 , the pK a of (Me 3 Si)NH in thf is 26, 31 depend critically on the solvent, concentration of the reactants, and temperature. These details are given in the Experimental Section, which are reproducable when close attention to detail is observed, and shown schematically in Scheme 1. Solutions of complexes Ce(tmtaa)(tmtaaH) (1) and Ce 2 tmtaa 3 (2) are extremely sensitive to trace amounts of air, which result in formation of Ce(tmtaa) 2 (3), which is stable to air and moisture. Deliberate oxidation of either 1 or 2 is therefore an excellent synthetic route to 3.Ce(tmtaa)(tmtaaH) (1) not when Ln = Ce. Crystals of Ce(tmtaa)(tmtaaH) grown from toluene, were twinned, the tmtaa and tmtaaH fragments are disordered, and therefore the X-ray diffraction pattern could not be resolved. However, the 2:1 stoichiometry of the complex is confirmed. Ce(tmtaa)(tmtaaH) (1) decomposes slowly to Ce(tmtaa) 2 (3) and tmtaaH 2 (ratio 1:1) in C 6 D 6 at 65 °C over 14 days. Close inspection of the decomposition process reveales that after one day small amounts of Ce 2 (tmtaa) 3 (2) and tmtaaH 2 are detected in the 1 H NMR spectrum. Over the time priod of two weeks the resonances due to 2 increase then decrease as 3 is formed and the resonances due to tmtaaH 2 continue to increase until a steady state is reached. The decomposition does not eliminate hydrogen since the latter is not observed in the 1 H NMR spectrum and the addition of dehydroanthracene does not yield anthracene. It seems reasonable to suggest that the initial decomposition step of 1 is the format...

A series of new tantalum-digol (digol = diethylene glycolate) complexes TaCp*Cl2(κ3-digol) (1), TaCp*Me2(κ3-digol) (2), TaCp*ClMe(κ3-digol) (3), and TaCp*Me(OTf)(κ3-digol) (OTf = triflate) (4) have been synthesized. Treatment of 2 with 1 equiv of H2O·B(C6F5)3 enabled the synthesis of a tantalum-oxo borane-stabilized complex, TaCp*{O·B(C6F5)3}(κ3-digol) (5). Insertion processes into the methyl groups of complexes 2, 3, and 4 were not observed upon reaction with CO or isocyanides. In contrast, complex 4 reacted slowly with 1 equiv of xylylisocyanide (xylyl = 2,6-dimethylphenyl) to yield the dicationic aminocarbene complex [TaCp*{C(Me)NH(xylyl)}(OH2)(κ3-digol)][OTf]2 (6). All products were characterized by NMR spectroscopy and elemental analysis. The single-crystal structures of 1, 5, and 6 were determined. The molecular structures of 1, 2, 3, and 6 were also determined by means of DFT-based methods.

A series of new tantalum-tbcp [tbcp = 2,2′-thiobis(4,6-dichlorophenolato)] and tantalum-tbop [tbop = 2,2′-thiobis(6-tert-octylphenolato)] complexes [TaCp*Cl2(κ3-tbop)] (1), [TaCp*Cl2(κ3-tbcp)] (2), [TaCp*Me2(κ3-tbop)] (3), [TaCp*Me2(κ3-tbcp)] (4), [TaCp*Me(κ3-tbop)(OTf)] (OTf = triflate) (5), [TaCp*Me(κ3-tbcp)(OTf)] (6), [TaCp*(κ3-tbop)(OTf)2] (7), and [TaCp*(κ3-tbcp)(OTf)2] (8) have been synthesized. Insertion processes into the methyl groups of complex 3 were not observed upon reaction with CO or isocyanides. In contrast, complex 4 reacted slowly with 1 equiv of xylyl isocyanide (xylyl = 2,6-dimethylphenyl) or tert-butyl isocyanide to yield complexes [TaCp*(κ2-Me2CNxylyl)(κ3-tbcp)] (9) and [TaCp*Me(κ2- MeCNtBu)(κ3-tbcp)] (10), respectively. All products were characterized by NMR spectroscopy and elemental analysis. The single-crystal structures of 2, 3, 6, and 9 were also determined.

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The complexes [Cp*TaMe(OCH 2 ) 2 py(H 2 O)]OTf (3), [Cp*Ta(OH)(OCH 2 ) 2 py(H 2 O)]OTf (4), and [Cp*Ta(OCH 2 ) 2 py-(H 2 O) 2 ]OTf 2 (5) are described as the first examples of watersoluble organometallic deriVatiVes of tantalum.

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