Hydridotris borate ligand

Hydridotris(3,5-dimethyl-l-pyrazolyl)borate]molybdenum-(i72-acyl) complexes, such as 1, are deprotonated by butyllithium or potassium hydride to generate enolate species, such as 488.8> jjie overa]] structure of these chiral complexes is similar to that of the iron and rhenium complexes discussed earlier the hydridotris(3,5-dimethyl-l-pyrazolyl)borate ligand is iso valent to the cyclopentadienyl ligand, occupying three metal coordination sites. However, several important differences must be taken into account when a detailed examination of the stereochemical outcome of deprotonation-alkylation processes is undertaken. 

Alkylation of enolates, such as 4, produces products that are consistent with the preferred approach of the electrophile from either the least hindered face of an T -cnolate of conformation C or the least hindered face of a Z-enolate of conformation D88. Steric factors influencing approach of the electrophile appear to be similar in both of these models since the steric bulk of the hydridotris(3,5-dimethyl-l-pyrazolyl)borate ligand and the phosphite are both considerable any stereoelectronic and dipolar factors due to interaction of the enolate ligand with the carbon monoxide ligand would likely be similar for both geometries. The is-enolate geometry C appears to benefit from reduced steric interactions between the R substituent and the metal ligands. 

Holmes, S. and CJ. Carrano. 1991. Models for the binding site in bromoperoxidase Mononuclear vanadium(V) phenolate complexes of the hydridotris(3,5-dimethylpyra-zolyl)borate ligand. Inorg. Chem. 30 1231-1235. 

A titanium complex with a pyrazolylborate ligand was studied by Campbell and Malanga [19]. Similarities between the cyclopentadienyl ligand and the hydridotris(pyrazolyl)borate ligand have been noted for transition metal complexes. Catalyst efficiencies are much lower than those of the analogous penta-methylcyclopentadienyl complexes. 

Vhf of 1-8 Hz between the 3-CF3 fluorines and the hydrogens of the platinum-bound methyl groups has been observed by Fekl et al in the spectrum of the novel platinum(IV) complex, Tp(CF3)2PtMe3, where Tp(CF3)2 denotes hydridotris(3,5-bis(trifluoromethyl)pyrazolyl)borate. This is the first example of a formal Vf h(-c) coupling in complexes involving hydridotris(pyr-azolyl)borate ligands... 

Chen C-K, Tong H-C, Chen Hsu C-Y, et al. Synthesis and reactivity of ruthenium azido complexes containing a hydridotris(pyrazolyl)borate ligand and dimerization of terminal alkynes in organic and aqueous media. Organometallics. 2009 28 3358-3368. 

Castro-Rodrigo R, Esteruelas MA, Lopez AM, Mozo S, Onate E. C-H bond activation reactions in p-allene-osmium-ttiisopropylphosphine complexes with cyclopentadienyl or hydridotris(pyrazolyl)borate ligands formation of isopropenyldiisopropylphosphine versus hydride-alkenylcarbyne derivatives. 

Tellers DM, Bergman RG. C—H bond activation by a rare cationic iridium dinitrogen complex. An important electronic effect in the chemistry of the hydridotris(pyrazolyl) borate ligand. /Am Chem Soc. 2000 122 954-955. 

The role of the cyclopentadienyl ligand in the a-bond activation of methane by [Co(ri -C5H5)] has been studied and a reaction mechanism proposed which includes several intermediates containing Co-alkyl bonds.A series of Ir-Me species have been synthesised as part of an investigation into the effect of the hydridotris(pyrazolyl)borate ligand on C-H bond activation by cationic iridium complexes. The rhodium species 23 has been synthesised as part of a study into... 

The C-C bond-forming coupling of solvent molecules via sp2- and r/ -C-H bond functionalizations can be achieved using an iridium complex based on the TpMe2 ligand (hydridotris(3,5-dimethylpyrazolyl)borate) (Equation (64)).65... 

The analogous coordination behavior of hydridotris(pyrazolyl)borate and tetrakis(pyrazolyl)-borate has been demonstrated by numerous reactions. Reduction of the rhenium(VII) complex [Re03 B(pz)4] with PPh3 in THF gives a reactive dimeric intermediate which reacted with monodentate and bidentate protic substrates to yield products with tridentate B(pz)4 ligands... 

Hydridotris(pyrazolyl)borates, as cobalt complex ligands, 44 274-278 Hydroboration, 16 230-234 chain lenghtening, 16 231-232 role in sythesis, 16 231, 232 Hydrocarbons clusters, 18 57-59... 

The hydridotris(pyrazolyl)borate (Tp) ligand has become well known and well established as a formal analogue of the cyclopentadienyl (Cp) ligand (43). Unlike Cp, however, when appropriately substituted, Tp can become what has been described (44, 45) as a tetrahedral enforcer ligand, producing complexes that are constrained to be tetrahedral even when other factors might allow octahedral coordination. 

Scheme 2.5 Ligands used to synthesize structural and/or functional models for iron enzymes containing a 2-His-l-carboxylate facial triad (a) R3TACN (TACN = 1,4,7-triazacyclononane) [25] (b) TpR,R [differently substituted hydridotris(pyrazol-l-yl)borates] [27] (c) differently substituted bis(pyrazol-l-yl)acetates [29] (d) differently substituted 3,3-bis(1 -alkylimidazol-2-yl)propionates [30],...

TCNE = Tetracyanoethylene Dipdba = 4,4 -diisopropyl(di-benzylideneacetone) TMM = Trimethylenemethane dppm = (Diphenylphosphino)methane MMLCT = Metal-metal bond to ligand charge-transfer Tp = Hydrido(trispy-razolyl)borate Tp = Hydridotris(3,5-dimethyl-pyrazolyl)bo-rate BAr = (3,5-triflnoromethylphenyl)borate ttab = l,2,4,5-tetrakis(l-iV-7-azaindolyl)benzene tmeda = Tetra-methylethylenediamine bpma = Bis(pyridyhnethyl)amine TFE = Triflnoroethanol dtbpm = Bis(di-terr-butylphosphi-no)methane dmpe = Bis(dimethylphosphino)ethane dcpe = Bis(dicyclohexylphosphino)ethane triphos = Bis(2-diphe-nylphosphinoethyl)phenylphosphine COD = 1,5-cycloocta-diene dppbts = (Diphenylphosphinobutane)tosylate sodium PPE = Poly(jo-phenylene ethylene). 

The NIR emission intensity of the lanthanide porphyrinate complexes follows the trend Yb > Nd > Er. This agrees with observations on other luminescent lanthanide complexes and reflects the fact that the efficiency of nonradiative decay increases as the energy of the luminescent state decreases. The emission yields of the ternary lan-thanide(III) monoporphyrinate complexes with hydridotris(pyrazol-l-yl)borate or (cyclopen-tadienyl)tris(diethylphosphito)cobaltate as a co-ligand are generally higher than those of other Yb(III), Nd(III), and Er(III) complexes because the coordination environment provided by the porphyrinate in combination with the tripodal anion effectively shields the Ln + ion from interacting with solvent (C-H) vibrational modes that enhance the rate of nonradiative decay. 

The anionic complexes [ j -CpM(CO)3] (M = Cr, Mo, W) react with alkyl halides to provide the air-sensitive complexes j -CpM(CO)3R . With respect to reaction with Mel, the relative nucleophilicities of these anions are in the order W > Mo > Cr . Anionic complexes in which the Cp ligand bears alkyl substituents as well as [TpMo(CO)3]" [Tp = hydridotris(pyrazolyl)borate] , behave analogously. The course of the reaction of [f7 -CpCr(CO)3] with allyl chlorides has been studied In diglyme, one cleanly obtains [>) -CpCr(CO)3]2 and coupling of allyl radicals . In THE, the reaction is somewhat more complex one obtains as the major product the same dimer, though a small amount of (jj -6-alkenylfulvene)Cr(CO)3 also forms . Presumably, the products are derived via initial formation of j -CpCr(CO)3( Callyl). 

A trispyrazolylborate ligand ([HB(C3N2H3)3], hydridotris (pyrazoyl)borate) a highly sterically bulky ligand used to protect metals from attack by other ligands... 

---