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The lithiation of 1,3-dipropoxy-p-tert-butylcalix[4]arene (LH2) followed by reaction with nBuMgBr in THF resulted in the formation of the hetero-bimetallic complex [Li(THF)Mg(nBu)L] (1). By contrast, the treatment of tripropoxy-p-tert-butylcalix[4]arene (L′H) with nBu2Mg afforded a mononuclear complex [L′Mg(nBu)] (2). Single-crystal XRD studies revealed that in both structures the calix[4]arene adopts a cone conformation, and a Li cation resides in the cavity for 1. Both 1 and 2 were active for the ring-opening polymerisation of rac-lactide. Compound 2 displayed not only exceptional activity (100 equivalents, 3 min, 92 % conversion, BnOH, room temperature) but also high selectivity (probability to form an r dyad, Pr=0.85) and exhibited an immortal character in THF. Surprisingly, compound 2 also showed isotactic bias (Pr=0.30–0.36) and an immortal character if toluene was employed as the solvent; 2 D J-resolved 1H NMR spectroscopy was employed for the assignment of the stereoselectivity.

The dimethylsulfide adduct of bis(pentafluorophenyl)borane HB(C 6 F 5 ) 2 ·SMe 2 reacts on mixing with alkenes such as 1-hexene and styrene, with selectivities closely following those of the Me 2 S-free reagent. The mono(pentafluorophenyl)borane H 2 B(C 6 F 5 )·SMe 2 also undergoes rapid hydroboration reactions to give the dialkylboranes R 2 B(C 6 F 5 ). Treatment of the boranes with trimethylsilylacetylene results in rapid hydroboration to give the trans-vinylborane. The reaction of H 2 B(C 6 F 5 )·SMe 2 with 1,5-cyclooctadiene at room temperature yields a kinetic mixture of the 1,4- and 1,5-dihydroboration products which quantitatively isomerizes on heating to the 1,5-isomer, pentafluorophenyl-9-borobicyclo[3.3.1]nonane. This bicyclic borane crystallizes as the SMe 2 adduct, which has been characterized by X-ray crystallography.

A new family of cyclometallated gold(III) thiolato complexes based on pyrazine‐centred pincer ligands has been prepared, (C^Npz^C)AuSR, where C^Npz^C=2,6‐bis(4‐ButC6H4)pyrazine dianion and R=Ph (1), C6H4 tBu‐4 (2), 2‐pyridyl (3), 1‐naphthyl (1‐Np, 4), 2‐Np (5), quinolinyl (Quin, 6), 4‐methylcoumarinyl (Coum, 7) and 1‐adamantyl (8). The complexes were isolated as yellow to red solids in high yields using mild synthetic conditions. The single‐crystal X‐ray structures revealed that the colour of the deep‐red solids is associated with the formation of a particular type of short (3.2–3.3 Å) intermolecular pyrazine⋅⋅⋅pyrazine π‐interactions. In some cases, yellow and red crystal polymorphs were formed; only the latter were emissive at room temperature. Combined NMR and UV/Vis techniques showed that the supramolecular π‐stacking interactions persist in solution and give rise to intense deep‐red photoluminescence. Monomeric molecules show vibronically structured green emissions at low temperature, assigned to ligand‐based 3IL(C^N^C) triplet emissions. By contrast, the unstructured red emissions correlate mainly with a 3LLCT(SR→{(C^Npz^C)2}) charge transfer transition from the thiolate ligand to the π⋅⋅⋅π dimerized pyrazine. Unusually, the π‐interactions can be influenced by sample treatment in solution, such that the emissions can switch reversibly from red to green. To our knowledge this is the first report of aggregation‐enhanced emission in gold(III) chemistry.

[(Me2S)Au]+ cations, generated from (Me2S)AuCl and AgSbF6 in dichloromethane at 0–20 °C, serve as sources of solvated Au+ (alongside unreactive [Au(SMe2)2]+), which reacts with the methyl-substituted arenes C6Me6–nHn (n = 0–2) with C–H bond cleavage to give the sulfonium salts [C6Me5–nHnCH2SMe2]+. There was no evidence for arene π coordination to Au+ or for the formation of σ-bonded Au–benzyl species. Surprisingly, the reaction of Au+ with CH2Ar2 leads to C–C bond cleavage (Ar = 2,4,6-C6H2Me3). The reactions are highly selective for benzylic C–H and C–C bonds, whereas metalation of the arene ring is not observed.

The borane dimethyl sulfide adduct H3B·SMe2 and the diethyl ether adduct of tris(pentafluorophenyl)borane, (C6F5)3B·OEt2, undergo facile exchange of hydride and pentafluorophenyl ligands, yielding (C6F5)2HB·SMe2 (1) and (C6F5)H2B·SMe2 (2) depending upon the ratio of reagents used. In the presence of excess dimethyl sulfide, both compounds can be isolated as colorless crystals, which have been structurally characterized.

The formation of cationic species relevant to olefin polymerization based on (SBI)HfCl2, Me2C(C5H4)(Flu)HfCl2, Ph2C(C5H4)(Flu)HfCl2, and L′HfCl2 activated by MAO, AlMe3/CPh3[B(C6F5)4], and AlBui3/CPh3[B(C6F5)4] (SBI = rac-Me2Si(Ind)2; L′ = C2H4(Flu)(5,6-C3H6-2-MeInd)) was studied by 1H, 13C, and 19F NMR spectroscopy. Thermally stable heterobinuclear intermediates of the type [LHf(μ-Me)2AlMe2]+[MeMAO]− and [LHf(μ-Me)2AlMe2]+[B(C6F5)4]− were identified when using MAO and AlMe3/CPh3[B(C6F5)4] as activators, respectively. The stability of these species explains the low productivity of hafnocene catalysts in the presence of AlMe3-containing activators, compared to zirconocenes. By contrast, in the ternary systems LHfCl2/AlBui3/CPh3[B(C6F5)4] hydride species were detected that must be responsible for the formation of the highly active sites in olefin polymerization. The ionic hydrido species differ significantly in stability. The formation of the mixed-alkyl complex L′Hf(Me)CH2SiMe3 proceeds with surprisingly h...

We report the first crystallographically characterized dimethylaniline complex of a group 4 metallocene. [(IPCF)ZrMe(NMe2Ph)][B(C6F5)4] shows strongly coordinated NMe2Ph which does not interchange in solution. DFT calculations suggest that the Zr-N bond is 23 kJ mol-1 stronger than the Zr-Me-Zr bond in [{(IPCF)ZrMe}2(µ-Me)][MeB(C6F5)3], the structure of which is also reported (IPCF = Me2C(C5H4)(fluorenyl)).

The mixed-alkyl metallocene complexes (IPCF)M(Me)(CH2SiMe3) (M = Zr, Hf; IPCF = Me2C(C5H4)(C13H8)) were synthesized by the reaction of (IPCF)M(Me)Cl (M = Zr, Hf) with Me3SiCH2MgCl. The crystal structures of (IPCF)Zr(CH2SiMe3)2, (IPCF)HfMe2, and (IPCF)Zr(Me)Cl were determined by X-ray diffraction. The kinetics of site epimerization of the ion pairs (IPCF)M(CH2SiMe3)(μ-Me)B(C6F5)3 and [(IPCF)MCH2SiMe3+···B(C6F5)4−] (M = Zr, Hf) were studied by variable-temperature NMR spectroscopy, while the solution ground-state structures of the ion pairs [LZrCH2SiMe3+···B(C6F5)4−] (L = SBI, IPCF; SBI = rac-Me2Si(Ind)2) were probed experimentally by 19F,1H HOESY NMR spectroscopy and theoretically by DFT and molecular dynamics calculations. They reveal differences in the strength of anion interactions between the SBI and IPCF systems which may be significant for their catalytic activity. The tetraarylborate salts are stabilized by agostic interactions to ligand Si−Me moieties, with Hf > Zr. The exchange rates of both the M...

Treatment of (C6F5)2Zn(toluene) with 2 equiv of a series of benzonitrile or pyridine derivatives yielded the complexes (C6F5)2Zn(L)2 (where L = benzonitrile, 4-(phenyl)benzonitrile, 4-(N-pyrrolyl)benzonitrile, pyridine, 4-(phenyl)pyridine, and 4-(N-pyrrolyl)pyridine). The four-coordinate solution-phase nature of these complexes was confirmed by a series of variable-temperature 19F NMR experiments and comparison to (C6F5)2Zn(2,2′-bipy). The solvent-free solid-state structures of each of the four-coordinate adducts and the toluene solvate of (C6F5)2Zn(NCC6H4C6H5)2 were determined by single-crystal X-ray diffraction and have distorted tetrahedral geometries. Analysis of the crystal packing revealed a preponderance of offset face-to-face homo−aryl and embrace-like interactions over the hetero−aryl, pentafluorophenyl−phenyl, interaction. These aryl−aryl synthons serve to assemble paired, one- and three-dimensional supramolecular architectures.

A series of eight adducts of the form (RR‘R‘ ‘N)2·Zn(C6F5)2 have been prepared through treatment of the Lewis acid Zn(C6F5)2 with 2 equiv of the corresponding amine (R = tBu or CH2Ph, R‘ = R‘ ‘ = H; R = R‘ = Me or CH2Ph, R‘ ‘ = H; R = Me, R‘ = CH2Ph, R‘ ‘ = H; RR‘ = cyclo-C4H8 or cyclo-C5H10, R‘ ‘ = H; R = R‘ = Me, R‘ ‘ = CH2Ph). The solid-state structures of all eight compounds have been elucidated by single-crystal X-ray diffraction. In each case the geometry about the zinc atom is essentially tetrahedral. However, there is considerable variation in the supramolecular architectures in the solid state. A number of types of noncovalent interactions are observed including phenyl−pentafluorophenyl stacking, X−H···F−C contacts, and offset face-to-face contacts between pentafluorophenyl rings, giving rise to one-, two-, and three-dimensional supramolecular structures. In our examples we find that no one intermolecular interaction predominates.

Treatment of the mono(salicylaldiminato)titanium complexes {3-But-2-(O)C6H3CHN(Ar)}TiCl3(THF) (Ar = C6H5, 2,4,6-Me3C6H2 or C6F5) with the potassium s-enaminoketonates (C6H5)NC(CH3)C(H)C(R)OK (R = CH3, CF3) yielded the first examples of heteroligated (salicylaldiminato) (s-enaminoketonato)titanium dichloride complexes. The complex {3-But-2-(O)C6H3CHN(C6H5)}{(C6H5)NC(CH3)C(H)C(CH3)O}TiCl2 was structurally characterized by X-ray diffraction and has an orientation with trans-O,O,cis-Cl,Cl, cis-N,N distorted octahedral geometry. These complexes polymerize ethene when activated with MAO; the highest productivity, 5650 kg PE (mol metal)-1 h-1 atm-1, was afforded by {3-But-2-(O)C6H3CHN(C6F5)}{(C6H5)NC(CH3)C(H)C(CF3)O}TiCl2 at 60 °C.

Treatment of Zr{3-Bu-t-2-(O)C6H3CH=N(C6C6F5))Cl-3(THF) with K[2-(C6H5NCH)C4H3N] yields Zr{3Bu(t)-2-(O)C6H3CH=N(C6F5)}{(2-(C6H5NCH)C4H3N)Cl-2, the first example of a (salicylaldiminato)(pyrrolylaldiminato)zirconium complex. The catalytic behavior of both the new zirconium pre-catalyst and its titanium analogue have been determined. The titanium system is the more effective catalyst for both ethene homopolymerization and copolymerizations with hex-1-ene, norbornene, and cyclopentene. The titanium catalyst combines the high productivities of the bis(salicylaldiminato) parent complex with the more favorable comonomer incorporation of the bis(pyrrolylaldiiminato) series.

N -ferrocenyl salicylaldimine (FcPI)H, readily accessible from aminoferrocene and salicylaldehyde, reacts with dibutylmagnesium in THF to afford a red crystalline (FcPI) 2 Mg(THF) 2 ( 2 ). The reactions of the Li(FcPI) with CpTiCl 3 gave CpTiCl 2 (FcPI) · CH 2 Cl 2 ( 4 ), whereas with CpZrCl 3 · DME a mixture of three products is formed: CpZrCl(FcPI) 2 ( 5 ), CpZrCl 2 (FcPI) ( 6 ), and (FcPI) 2 ZrCl 2 · CH 2 Cl 2 ( 3 · CH 2 Cl 2 ). The crystal structures of compounds 2 – 6 are reported. Typically, the N–O chelates are oriented such that O donors are mutually trans , while N donors prefer to be trans to Cl ligands. The redox potentials of these complexes are very similar to ferrocene. On activation with methylaluminoxane, the Ti complex 4 shows moderate activity for ethylene polymerisation, while (FcPI) 2 ZrCl 2 is highly active for the oligomerisation of ethylene, to give products with average degrees of polymerisation of 12–16.

Reactive intermediates in living olefin polymerization over homogeneous catalysts based on bis[N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato]titanium(IV) dichloride (L2TiCl2) have been studied. Outer sphere ion pairs [L2TiMe(S)]+[Me-MAO]- and [L2TiMe(S)]+[B(C6F5)4]- (S = solvent molecule), formed by activation of L2TiCl2 with MAO or with AlMe3/[CPh3]+[B(C6F5)4]-, and reactions of these ion pairs with ethene to afford chain-propagating species [L2TiP]+[Me-MAO]- and [L2TiP]+[B(C6F5)4]- (P = growing polymeryl chain) have been characterized by 1H, 13C, and 19F NMR spectroscopy.

The new mixed-alkyl metallocene complexes (SBI)M(Me)CH2SiMe3 (M = Zr, Hf) are accessible by the successive treatment of (SBI)MCl2 with Me3SiCH2MgCl and MeMgCl in toluene (SBI = rac-Me2Si(1-Ind)2). Reaction with B(C6F5)3 or CPh3+[B(C6F5)4]- in toluene or toluene/difluorobenzene affords (SBI)Mδ+(CH2SiMe3)(μ-Me)Bδ-(C6F5)3 and the ion pairs [(SBI)MCH2SiMe3+···B(C6F5)4-], respectively. Both types of compounds are thermally stable in aromatic solvents at ambient temperature. Whereas in the MeB(C6F5)3- complexes the alkyl ligand points away from the metal and tight anion coordination forms the familiar inner-sphere ion pair, in the B(C6F5)4- salts the alkyl ligand adopts a conformation that enables agostic bonding to a γ-CH3 group. Here, and by implication in M-polymeryl species of similar steric requirements, agostic interactions are preferred over anion coordination, leading to an outer-sphere ion pair structure. This alkyl bonding mode retards the −SiMe3 rotation, which for M = Hf is slow on the NMR time scal...

The Schiff base N,N‘-o-phenylenebis(3,5-di-tert-butyl-salicylideneimine) (1; tBu4salophenH2) reacts with 1 equiv of Zr(η5-C5H5)Cl3·DME in the presence of 2.2 equiv of NEt3 in pentane to give the monocyclopentadienyl bis(phenoxo-imino) monochloro zirconium derivative Zr(η5-C5H5)[C6H4-1,2-{NCH(3,5-tBu2C6H2-2-O)}2]Cl (2). Moreover, 2 equiv of the monolithiated reagent derived from 3-tert-butyl-N-ethylsalicylaldimine by reaction with LinBu in hexane reacts at −78 °C with 1 equiv of Zr(η5-C5H5)Cl3·DME in THF to yield the corresponding monocyclopentadienyl bis(phenoxo-imino) monochloro zirconium complex Zr(η5-C5H5)[CH3CH2NCH{(3-tBuC6H3-2-O)}]2Cl (5) after elimination of LiCl. Methylation of 2 with MgClMe in pentane or toluene at −78 °C affords Zr(η5-C5H5)[1,2-C6H4{NCH(3,5-tBu2C6H2-2-O)}{NCH(Me)(3,5-tBu2C6H2-2-O)}] (3) as a result of the reduction of one of the CN bonds of the coligand. The hydrolysis of 3 gives the new organic compound [C6H4{NCH(3,5-tBu2C6H2-2-OH)}{NCH(Me)(3,5-tBu2C6H2-2-OH)}] (4), which was al...

The influence of perfluoroborate anions on catalyst activity and stereospecificity has been determined for propene polymerisations at 20-60°C. For C 2 -symmetric ansa-zirconocenes, activities were strongly ligand-dependent, with systems activated by TIBA/Ph 3 C + X ― , where TIBA=A1 i BU 3 , X={Z[B(C 6 F 5 ) 3 ] 2 }, and Z=CN or NH 2 , giving significantly higher activities than methylaluminoxane under comparable conditions. For high-activity catalysts at 60°C, {H 2 N[B(C 6 F 5 ) 3 ] 2 } - proved superior to {CN[B-(C 6 F 5 ) 3 ] 2 } - , presumably due to the higher thermal stability of the amidoborate. The influence of couteranions on PP stereospecificity for these catalysts is negligible. On the other hand, the conformationally flexible catalyst, (2-PhInd) 2 Zr-C1 2 /TIBA/Ph 3 C + X - , shows not only a strong anion dependence of its activity, but also significant variation in poly(propylene) isotacticity, mainly due to the formation of small fractions of highly isotactic (mmm>70%)PP. This effect was particularly pronounced for {CN[B(C 6 F 5 ) 3 ] 2 } - and the dianion, {Ni[CNB(C 6 F 5 ) 3 ] 4 } 2

The reaction of Cp'(CpB)ZrCl2 [CpB=?5-C5H4B(C6F5)2] with LiNHCMe3 gave Cp'(CpB)(µ-NHCMe3)ZrCl, with a constrained-geometry type Cp---B---N chelate ligand. The 19F-NMR spectrum of the zirconium complexes, as well as that of the titanium analogue, reveals C---F...H---N hydrogen bonding to one of the ortho-F atoms of a C6F5 ring, strong enough to persist in solution at room temperature. The reaction of Cp'(CpB)TiCl2 with LiPPh2 affords the Cp---B---P chelate complex Cp'(CpB)(µ-PPh2)TiCl, the first example of a crystallographically characterised Ti(IV) phosphido compound. A 19F-NMR study of a number of adducts of B(C6F5)3 with prim- and sec-amines demonstrates the importance of intramolecular hydrogen bonding to C6F5 in this class of compounds, while there are no such interactions in B(C6F5)3(PHR2) (R=Cy, Ph). The crystal structures of Cp'(CpB)(µ-PPh2)TiCl, B(C6F5)3(NHMe2) and B(C6F5)3(PHCy2) are reported.

Deprotonation of the phenol-imines 2-But-6-(RNCH)C6H3OH (R=2,4,6-Me3C6H2 (1a), C6F5 (1b), C6H11 (1c) and phenol-amines 2,4-But2-6-(R′NCH2)C6H2OH (R′=C4H8 (1d), C5H10 (1e)) with n-BuLi gives the corresponding lithium phenoxides. The reaction with MCl4 in THF solution leads to the bis(ligand) complexes {2-But-6-(RNCH)C6H3O}2MCl2 and {2,4-But2-6-(R′NCH2)C6H2O}2MCl2 (M=Ti: 2a, 2d, 2e, Zr: 3a, 3d and 3e). The cyclopentadienyl phenoxy-imine and -amine complexes Cp{2-But-6-(RNCH)C6H3O}MCl2 and Cp{2,4-But2-6-(R′NCH2)C6H2O}MCl2 (M=Ti: 4a–4e, Zr: 5a–5e) were prepared similarly through reaction with CpMCl3. The crystal and molecular structures of 2a, 3a, 4a and 4e have been determined. 2a and 3a are isostructural and exhibit a distorted octahedral geometry. 4a has a distorted square-pyramidal structure whereas 4e is essentially tetrahedral and the nitrogen does not coordinate. All new complexes are active for the polymerisation of ethene when activated with methyaluminoxane. 4b, 5a, 5d and 5e are active for the copolymerisation of ethene and 1-hexene and the oligomerisation of 1-hexene.

The ansa-borane complex (Me2S)(C6H5)B(C5H4)2ZrCl2 ( 1 ) reacts selectively with 2 equiv of LiC6F5 to give (Me2S)(C6H5)B(C5H4)2Zr(C6F5)2 ( 2 ) and with 3 equiv LiC6F5 to form the borato-bridged complex [Li(Et2O)3][(C6F5)(C6H5)B(C5H4)2Zr(C6F5)2] ( 3a ). The C6F5 groups are exchanged for Me by reaction with AlMe3 to form [Li(Et2O)x][(C6F5)(C6H5)B(C5H4)2ZrMe2] ( 4 ). Treatment of BCl3 with (SiMe3)(SnMe3)C5H4 affords BCl(C5H4SiMe3)2 ( 5 ), which undergoes a dehalosilylation reaction with ZrCl4(Me2S)2 to give Cl(Me2S)B(C5H4)ZrCl2 ( 6 ). The reaction of 6 with LiC6F5 proceeds in a fashion similar to that of 2 , leading first to (Et2O)ClB(C5H4)2Zr(C6F5)2 ( 7 ) and with 5 equiv of LiC6F5 to [Li(Et2O)4][(C6F5)2B(C5H4)2Zr(C6F5)2] ( 9a ) in 28% yield. The yield is improved through the use of C6F5MgBr at 60 °C. The C6F5 groups are readily exchanged for Me through reaction with LiMe to give [Li(Et2O)4][(C6F5)2B(C5H4)2ZrMe2] ( 10a ). Complexes 3 , 9 , and 10 are catalysts for ethene polymerization when activated with MAO or AlBui3/[CPh3][B(C6F5)4].

The (borylcyclopentadienyl)titanium complex (Cp-B)TiCl3 (1; Cp-B = eta(5)-C5H4B(C6F5)(2)) reacts with LiC5H5 (LiCp), LiC5H4SiMe3 (LiCP'), and LiC9H7 (LiInd) to give the titanocene complexes (Cp-B)CpTiCl2 (2), (Cp-B)Cp'TiCl2 (3), and (Cp-B)(Ind)TiCl2 (4), respectively. In contrast to 1, which possesses piano stool geometry with an uncoordinated, trigonal-planar borg moiety, the -B(C6F5)(2) substituents in 2-4 act as intramolecular Lewis acids by coordinating to chloride ligands, with formation of B-Cl-Ti bridges that have relatively short B-Cl and elongated Ti-Cl bonds. The compounds are fluxional, with the -B(C6F5)(2) moiety switching rapidly from one chloride ligand to the other (2: Delta G(double dagger) = 37 kJ mol(-1) (200 K)). Recrystallization of 2 in the presence of traces of moisture afforded (Cp-B)CpTi(mu-OH)Cl (5), with a rigid B-O-Ti chelate arrangement. Treatment of 1 with 1 or 2 equiv of LiHNCMe3 gives the binuclear titanium imido complexes [(Cp-B)TiCl(mu-NCMe3)](2) (7) and [(Cp-B)TiCl(mu-NCMe3). H2NCMe3](2) (8), respectively. These complexes are based on Ti2N2 rings but show no boron-imide interactions. In contrast, the reaction of 2 with LiNHCMe3 affords (Cp-B)CpTi(mu-NHCMe3)Cl (9), which exhibits a constrained-geometry type Cp-B-N arrangement. The crystal structures of 4, 5, 8, and 9 have been determined.

Metallocene complexes of Group 4 metals are playing an increasingly important role in olefin polymerisation catalysis. This contribution surveys several aspects of the chemistry of metallocene catalysts that are being pursued in our laboratory at present, namely the application of half-sandwich complexes as catalysts for high-molecular weight elastomeric polypropene, unusual C–H activation reactions of zirconium half-sandwich complexes, the development of 14-electron borole complexes as neutral analogues of cationic [Cp 2 ZrR] + catalysts, and the heterogenisation of MAO-free zirconocene catalysts on borate-functionalised silica.

Bis(pentafluorophenyl)boron fluoride (C6F5)2BF·OEt2 (1), readily accessible from BF3·OEt2 and 2 equiv of C6F5MgBr, reacts with fluorenyllithium to give (Flu)B(C6F5)2 (4), while the reaction with indenyllithium leads to the regioisomers 1- and 2-IndB(C6F5)2 5 and 6, which are separated by fractional crystallization. 4 and 5 form crystalline adducts with tert-butylamine. The trimethylsilyl derivatives Flu(SiMe3)B(C6F5)2 (9) and Ind(SiMe3)B(C6F5)2 (10) are similarly prepared. Heating (C6F5)2BF·OEt2 leads to ether cleavage and formation of (C6F5)2BOEt. Treatment of 5 and 6 with Zr(NMe2)4 at room temperature gives indenylzirconium amido half-sandwich complexes; however, the reaction is accompanied by the unexpected exchange of one boron-C6F5 substituent by NMe2, to form 1- and 2-{C9H6B(C6F5)(NMe2)}Zr(NMe2)3. Reaction with SiClMe3 affords the trichlorides 1- and 2-{C9H6B(C6F5)(NMe2)}ZrCl3. The NMe2 substituent reduces the Lewis acidity of boron, so that donor ligands such as THF or DME coordinate exclusively to...

Bis(cyclopentadienyl)hafnium diethyl (1) reacts with [CPh3][B(C6F5)4] in dichloromethane at −60 °C with hydride rather than alkyl transfer to give triphenylmethane and the ethyl-bridged dinuclear complex [(Cp2HfEt)2(μ-Et)][B(C6F5)4] (2). The complex is less stable than analogous methyl complexes but is stabilized by the presence of excess Cp2HfEt2. The reaction between Cp2HfEt2, [CPh3][B(C6F5)4], and AlEt3 under analogous conditions leads to [Cp2Hf(μ-Et)2AlEt2][B(C6F5)4] (3). The reaction between Cp2 HfMe2 and AlEt3 leads to alkyl ligand exchange to give, successively, Cp2Hf(Me)(Et) and Cp2 HfEt2. Similar fast ligand exchange reactions, take place between Cp′2ZrMe2 and AlEt3 and can be used for generating the thermally labile complex Cp′2ZrEt2 as a precursor for cationic polymerization catalysts [Cp′2 = Cp2, rac-Me2Si(Ind)2]. Polymerization activities of rac-[Me2Si(Ind)2Zr(μ-R)2AlR2][B(C6F5)4] increase in the order R = Me

Treatment of Me(2)S·B(C(6)F(5))(n) H(3-n) (n=1 or 2) with ammonia yields the corresponding adducts. H(3)N·B(C(6)F(5))H(2) dimerises in the solid state through N-H···H-B dihydrogen interactions. The adducts can be deprotonated to give lithium amidoboranes Li[NH(2)B(C(6)F(5))(n)H(3-n)]. Reaction of the n=2 reagent with [Cp(2)ZrCl(2)] leads to disubstitution, but [Cp(2)Zr{NH(2)B(C(6)F(5))(2)H}(2)] is in equilibrium with the product of β-hydride elimination [Cp(2)Zr(H){NH(2)B(C(6)F(5))(2)H}], which proves to be the major isolated solid. The analogous reaction with [Cp(2)HfCl(2)] gives a mixture of [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)] and the N-H activation product [Cp(2)Hf{NHB(C(6)F(5 )(2)H}]. [Cp(2)Zr{NH(2)B(C(6)F(5))(2)H}(2)]·PhMe and [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)]·4(thf) exhibit β-B-agostic chelate bonding of one of the two amidoborane ligands in the solid state. The agostic hydride is invariably coordinated to the outside of the metallocene wedge. Exceptionally, [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)]⋅PhMe has a structure in which the two amidoborane ligands adopt an intermediate coordination mode, in which neither is definitively agostic. [Cp(2)Hf{NHB(C(6)F(5))(2)H}] has a formally dianionic imidoborane ligand chelating through an agostic interaction, but the bond-length distribution suggests a contribution from a zwitterionic amidoborane resonance structure. Treatment of the zwitterions [Cp(2)MMe(μ-Me)B(C(6)F(5))(3)] (M=Zr, Hf) with Li[NH(2)B(C(6)F(5))(n)H(3-n)] (n=2) results in [Cp(2) MMe{NH(2)B(C(6)F(5))(2)H}] complexes, for which the spectroscopic data, particularly (1)J(B,H), again suggest β-B-agostic interactions. The reactions proceed similarly for the structurally encumbered [Cp''(2)ZrMe(μ-Me)B(C(6)F(5))(3)] precursor (Cp''=1,3-C(5)H(3)(SiMe(3))(2) , n=1 or 2) to give [Cp''(2)ZrMe{NH(2)B(C(6)F(5))(n)H(3-n)}], both of which have been structurally characterised and show chelating, agostic amidoborane coordination. In contrast, the analogous hafnium chemistry leads to the recovery of [Cp''(2)HfMe(2)] and the formation of Li[HB(C(6)F(5))(3)] through hydride abstraction.

In response to a recent paper concerning the formation of a putative arene complex, [Cp* 2 Zr(CH 3 )η-C 6 H 5 C(C 6 H 5 ) 2 CH 3 ][B(C 6 F 5 ) 4 ] from the reaction of Cp* 2 ZrMe 2 with [CPh 3 ][B(C 6 F 5 ) 4 ] in CD 2 Cl 2 at −78 °C, we present data showing that this reaction leads in fact to a mixture of [(Cp* 2 ZrMe) 2 (μ-Me)][B(C 6 F 5 ) 4 ] and [Cp* 2 ZrMe⋯B(C 6 F 5 ) 4 ], while NMR signals attributed to η-arene coordination of triphenylethane are due to unreacted CPh 3 + (Cp*=η-C 5 Me 5 ).

The reaction between NaNH2 and B(C6F5)3 affords the amidodiborate anion [H2N{B(C6F5)3}2]-, the structure of which shows multiple intramolecular NH···F hydrogen bonding. Reaction with HCl affords [H(OEt2)2][H2N{B(C6F5)3}2], while treatment of zirconocene dimethyls with [CPh3][H2N{B(C6F5)3}2] gives highly active alkene polymerization catalysts.

Treatment of Cp(2)HfCl(2) with two equivalents of LiNH(2)BH(C(6)F(5))(2) in toluene solution yields Cp(2)Hf{NHBH(C(6)F(5))(2)}, which has been crystallographically characterised. The otherwise base-free [NHBH(C(6)F(5))(2)] complex is stabilised by an agostic interaction.

The reaction of CP′2MMe2 (M  Ti, Zr, or Hf) with either [CPh3]+ or [PhNHEt2]+ salts of non-coordinating anions gives new cationic [Cp′2MMe]+ catalysts. The ethene polymerisation activity increases in the order M  Ti « Hf

Treatment of the homoleptic titanium amides [Ti(NR(2))(4)] (R=Me or Et) with the Bronsted acidic reagent H(3)NB(C(6)F(5))(3) results in the elimination of one molecule of amine and the formation of the four-coordinate amidoborate complexes [Ti(NR(2))(3){NH(2)B(C(6)F(5))(3)}], the identity of which was confirmed by X-ray crystallography. The reaction with [Zr(NMe(2))(4)] proceeds similarly but with retention of the amine ligand to give the trigonal-bipyramidal complex [Zr(NMe(2))(3){NH(2)B(C(6)F(5))(3)}(NMe(2)H)]. Cyclopentadienyl (Cp) amidoborate complexes, [MCp(NR(2))(2){NH(2)B(C(6)F(5))(3)}] (M=Ti, R=Me or Et; M=Zr, R=Me) can be prepared from [MCp(NR(2))(3)] and H(3)NB(C(6)F(5))(3), and exhibit greater thermal stability than the cyclopentadienyl-free compounds. H(3)NB(C(6)F(5))(3) reacts with nBuLi or LiN(SiMe(3))(2) to give LiNH(2)B(C(6)F(5))(3), which complexes with strong Lewis acids to form ion pairs that contain weakly coordinating anions. The attempted synthesis of metallocene amidoborate complexes from dialkyl or diamide precursors and H(3)NB(C(6)F(5))(3) was unsuccessful. However, LiNH(2)B(C(6)F(5))(3) does react with the highly electrophilic reagents [MCp(2)Me(mu-Me)B(C(6)F(5))(3)] to give [MCp(2)Me(mu-NH(2))B(C(6)F(5))(3)] (M=Zr or Hf). Comparison of the molecular structures of the Group 4 amidoborate complexes reveals very similar B--N, Ti--N and Zr--N bond lengths, which are consistent with a description of the bonding as a dative interaction between an {M(L)(n)(NH(2))} fragment and the Lewis acid B(C(6)F(5))(3). Each of the structures has an intramolecular hydrogen-bonding arrangement in which one of the nitrogen-bonded hydrogen atoms participates in a bifurcated FHF interaction to ortho-F atoms.

Cation exchange of [Li(THF)4]+[C5H5B(C6F5)3]- with [NEt4][BF4] gives the stable, ether-free salt [NEt4][C5H5B(C6F5)3], which reacts cleanly with Zr(NMe2)4 to afford [NEt4][{C5H4B(C6F5)3}Zr(NMe2)3] in good yield. The triamide is readily converted into the crystallographically characterized dimeric trichloride [NEt4]2[{C5H4B(C6F5)3}Zr(μ-Cl)Cl2]2.

The reaction between B(C(6)F(5))(3) and NH(3)(g) in light petroleum yielded the solvated adduct H(3)N.B(C(6)F(5))(3).NH(3). Treatment with a second equivalent of B(C(6)F(5))(3) afforded H(3)N.B(C(6)F(5))(3). Attempts to prepare the analogous alane adduct were unsuccessful and resulted in protolysis. Related compounds of the form R'R' 'N(H).M(C(6)F(5))(3) were synthesized from M(C(6)F(5))(3) and the corresponding primary and secondary amines (M = B, Al; R' = H, Me, CH(2)Ph; R' ' = Me, CH(2)Ph, CH(Me)(Ph); R'R' ' = cyclo-C(5)H(10)). The solid-state structures of 13 new compounds have been elucidated by single-crystal X-ray diffraction and are discussed. Each of the borane adducts has a significant bifurcated intramolecular hydrogen bond between an amino hydrogen and two o-fluorines, while N-H...F-C interactions in the alane adducts are weaker and more variable. (19)F NMR studies demonstrate that the borane adducts retain the bifurcated C-F...H...F-C hydrogen bond in solution. Compounds of the type R'R' 'N(H).M(C(6)F(5))(3) conform to Etter's rules for the prediction of hydrogen-bonding interactions.

The reactions between the cyclic sec. amines pyrrolidine and piperidine with B(C6F5)3 yield Lewis acid-base adducts with both intra- and inter-molecular hydrogen bonding interactions between C–H and N–H groups and aryl-fluorines in the solid state.

Octahedral titanium and zirconium complexes based on salicyloxazoline ligands with sterically demanding ortho-substituents provide a new family of extremely active ethene polymerization catalysts [up to 10(8) g PE (mol bar h)(-1)] which are in some cases "single site".

The mono(salicylaldiminato) complexes Ti{3-tBu-2-(O)C6H3CHN(R)}Cl3(THF) (where R = C6H5, C6F5) react with the metallated pyrrolylaldiminato ligand, K[2-(C6H5NCH)C4H3N], to afford the first examples of hybrid salicylaldiminato-ligated octahedral titanium complexes; the pre-catalysts give from very high to extremely high ethene polymerisation productivities when activated with MAO.

Borate-substituted di- and tri-anionic cyclopentadienyi ligands [X3B–C5H4]2– and [X2B(C5H4)2]3–-(X = C6F5) give anionic group 4 metallocene complexes which provide a facile route to zwitterionic ‘single-component’ alkene polymerisation catalysts.