Interaction of Metal Oxido Compounds with B(C6 F5 )3

Lewis acid-base pair chemistry has been placed on a new level with the discovery that adduct formation between an electron donor (Lewis base) and acceptor (Lewis acid) can be inhibited by the introduction of steric demand, thus preserving the reactivity of both Lewis centers, resulting in highly unusual chemistry. Some of these highly versatile frustrated Lewis pairs (FLP) are capable of splitting a variety of small molecules, such as dihydrogen, in a heterolytic and even catalytic manner. This is in sharp contrast to classical reactions where the inert substrate must be activated by a metal-based catalyst. Very recently, research has emerged combining the two concepts, namely the formation of FLPs in which a metal compound represents the Lewis base, allowing for novel chemistry by using the heterolytic splitting power of both together with the redox reactivity of the metal. Such reactivity is not restricted to the metal center itself being a Lewis acid or base, also ancillary ligands can be used as part of the Lewis pair, still with the benefit of the redox-active metal center nearby. This Minireview is designed to highlight the novel reactions arising from the combination of metal oxido transition-metal or rare-earth-metal compounds with the Lewis acid B(C₆ F₅ )₃ . It covers a wide area of chemistry including small molecule activation, hydrogenation and hydrosilylation catalysis, and olefin metathesis, substantiating the broad influence of the novel concept. Future goals of this young and exciting area are briefly discussed.

Titanium(IV) and Zirconium(IV) Sulfato Complexes Containing the Kläui Tripodal Ligand: Molecular Models of Sulfated Metal Oxide Surfaces

Treatment of titanyl sulfate in about 60 mM sulfuric acid with NaL(OEt) (L(OEt) (-)=[(eta(5)-C(5)H(5))Co{P(O)(OEt)(2)}(3)](-)) afforded the mu-sulfato complex [(L(OEt)Ti)(2)(mu-O)(2)(mu-SO(4))] (2). In more concentrated sulfuric acid (>1 M), the same reaction yielded the di-mu-sulfato complex [(L(OEt)Ti)(2)(mu-O)(mu-SO(4))(2)] (3). Reaction of 2 with HOTf (OTf=triflate, CF(3)SO(3)) gave the tris(triflato) complex [L(OEt)Ti(OTf)(3)] (4), whereas treatment of 2 with Ag(OTf) in CH(2)Cl(2) afforded the sulfato-capped trinuclear complex [{(L(OEt))(3)Ti(3)(mu-O)(3)}(mu(3)-SO(4)){Ag(OTf)}][OTf] (5), in which the Ag(OTf) moiety binds to a mu-oxo group in the Ti(3)(mu-O)(3) core. Reaction of 2 in H(2)O with Ba(NO(3))(2) afforded the tetranuclear complex (L(OEt))(4)Ti(4)(mu-O)(6) (6). Treatment of 2 with [{Rh(cod)Cl}(2)] (cod=1,5-cyclooctadiene), [Re(CO)(5)Cl], and [Ru(tBu(2)bpy)(PPh(3))(2)Cl(2)] (tBu(2)bpy=4,4'-di-tert-butyl-2,2'-dipyridyl) in the presence of Ag(OTf) afforded the heterometallic complexes [(L(OEt))(2)Ti(2)(O)(2)(SO(4)){Rh(cod)}(2)][OTf](2) (7), [(L(OEt))(2)Ti(O)(2)(SO(4)){Re(CO)(3)}][OTf] (8), and [{(L(OEt))(2)Ti(2)(mu-O)}(mu(3)-SO(4))(mu-O)(2){Ru(PPh(3))(tBu(2)bpy)}][OTf](2) (9), respectively. Complex 9 is paramagnetic with a measured magnetic moment of about 2.4 mu(B). Treatment of zirconyl nitrate with NaL(OEt) in 3.5 M sulfuric acid afforded [(L(OEt))(2)Zr(NO(3))][L(OEt)Zr(SO(4))(NO(3))] (10). Reaction of ZrCl(4) in 1.8 M sulfuric acid with NaL(OEt) in the presence Na(2)SO(4) gave the mu-sulfato-bridged complex [L(OEt)Zr(SO(4))(H(2)O)](2)(mu-SO(4)) (11). Treatment of 11 with triflic acid afforded [(L(OEt))(2)Zr][OTf](2) (12), whereas reaction of 11 with Ag(OTf) afforded a mixture of 12 and trinuclear [{L(OEt)Zr(SO(4))(H(2)O)}(3)(mu(3)-SO(4))][OTf] (13). The Zr(IV) triflato complex [L(OEt)Zr(OTf)(3)] (14) was prepared by reaction of L(OEt)ZrF(3) with Me(3)SiOTf. Complexes 4 and 14 can catalyze the Diels-Alder reaction of 1,3-cyclohexadiene with acrolein in good selectivity. Complexes 2-5, 9-11, and 13 have been characterized by X-ray crystallography.

Coordination chemistry of novel scorpionate ligands based on 3-cyclohexylpyrazole and 3-cyclohexyl-4-bromopyrazole

The ligands [hydrotris(3-cyclohexylpyrazol-1-yl)borate, [Tp(Cy)](-), tetrakis(3-cyclohexylpyrazol-1-yl)borate, [pz(o)Tp(Cy)](-), and hydrotris(3-cyclohexyl-4-bromopyrazol-1-yl)borate, [Tp(Cy,4Br)](-) were synthesized and characterized as their Tl(I) derivatives. They were converted to a variety of tetrahedral LMX and octahedral LML' complexes, as well as to the dinuclear nickel carbonate complex [Ni(Tp(Cy))](2)(CO(3)), 4, and the compound Ni[Tp(Cy,4Br)][pz(Cy,4Br)](3)(H)(2), 5. The structures of Co[Tp(Cy)]Cl, 1, Co[Tp(Cy,4Br)]Cl, 2, Co[Tp(Cy,4Br)]NCS, 3, [Ni(Tp(Cy))](2)(CO(3)), 4, Ni[Tp(Cy,4Br)][pz(Cy,4Br)](3)(H)(2), 5, and Mo[Tp(Cy)](CO)(2)(eta(3)-methallyl), 6, were determined by X-ray crystallography. The structures of paramagnetic heteroleptic complexes Co[Tp(Cy)][Tp], Co[Tp(Cy)][Tp], Co[Tp(Cy,4Br)][Tp], and Co[Tp(Cy,4Br)][Tp] were established by NMR. The homoleptic compounds Co[Tp(Cy)](2) and Co[Tp(Cy,4Br)](2) rearrange thermally to Co[Tp(Cy)](2) and to Co[Tp((Cy,4Br))](2), respectively, containing one 5-cyclohexyl group/ligand.

Synthesis and Complexation Properties of the Anions (eta(5)-C(5)Me(5))Ru(PR(2)O)(3)(2)(-) as Ligands

Reaction of [(eta(5)-C(5)Me(5))Ru(OMe)](2) (2) with HP(O)(OR)(2) gave the novel tripod ligands H(2)(eta(5)-C(5)Me(5))Ru{PO(OR)(2)}(3) (R = Me, Et, (i)Pr, H(2)1). H(2)(eta(5)-C(5)Me(5))Ru{PO(Ph(2))}(3) was formed with HP(O)Ph(2). [(eta(5)-C(5)Me(5))RuCl(2)](2) (3) with NaP(O)(OEt)(2) similarly gave Na(2)(eta(5)-C(5)Me(5))Ru{PO(OEt)(2)}(3) (Na(2)1; Na(2)L). Either the hydrogen form or the sodium salt was reacted with main group and transition metal halides to yield complexes [ML(2)](n)()(-) (M = Si(IV), Ti(IV), Nb(IV), n = 0; Co(II), n = 2; Cr(III), Fe(III), n = 1), or complexes of the form LMX with MX = BPh, VO. Reaction of Na(2)(eta(5)-C(5)Me(5))Ru{PO(Ph(2))}(3) with TiCl(4) gave intermediately [LTiCl(2)](2) which readily hydrolyzed on chromatography over Al(2)O(3) to trinuclear (LTiO)(3)(&mgr;(3)-O)H(2). The latter was characterized by X-ray structure analysis. It crystallizes in the cubic space group Pa3 (No. 205), z = 8, a = 30.83(1) Å, V = 29300(30) Å(3). From the reaction of Na(2)1 and 3 under appropriate conditions, the mixed valence complex LRu(eta(5)-C(5)Me(5)) (4) was isolated. Compounds were characterized by spectroscopy and electrochemistry. From absorption spectra of the Co(II) and the Cr(III) complex ligand field parameters Delta(o) = 902 and 1450 cm(-)(1), respectively, were derived, placing 1 near F(-) in the spectrochemical series.

Das Cäsiumsalz eines polydentaten Sauerstoffliganden. Synthese und zweidimensionale Schichtstruktur von Cs[(C5H5)Co{PO(OCH3)2}3]

The Cs salt CsLoMe ≡ Cs[(C5H5)Co{PO(OCH3)2}3] was obtained from the chloride of the diprotonated ligand LoMe and CsOH · H2O. Crystals were grown from a mixture of 1,2-dichloroethane/diethylether. They belong to the monoclinic space group P2l/c with lattice parameters a = 12.390(4) Å, b = 12.223(8) Å, c = 13.248(8) Å, β = 100.58(4)°. The structure was solved by Patterson and Difference Fourier methods. Refinement converged at R = 0.063, Rw = 0.071 for 2110 reflections and 227 parameters. The Cs ions show eightfold coordination and form a two-dimensional layer structure parallel to the crystallographic (100) plane.