A bis(phosphinimino)methanide lanthanum amide as catalyst for the hydroamination/cyclisation, hydrosilylation and sequential hydroamination/hydrosilylation catalysis

[La[N(SiHMe2)2]2[CH(PPh2NSiMe3)2]], which was obtained via an amine elimination starting from [CH2(PPh2NSiMe3)2] and [La[N(SiHMe2)2]3(THF)2], was used as catalyst for the hydroamination/cyclisation, the hydrosilylation and the sequential hydroamination/hydrosilylation reaction.     

Yttrium and lanthanide complexes with various P,N ligands in the coordination sphere: synthesis, structure, and polymerization studies

Yttrium and lanthanide complexes with different P,N ligands in the coordination sphere have been synthesized. First the chloride complexes [{CH(PPh2NSiMe3)2}Ln{(Ph2P)2N}Cl] (Ln = Y (1 a), La (1 b), Nd (1 c), Yb (1 d)) having the bulky [CH(PPh2NSiMe3)2]- and the flexible [(Ph2P)2N]- ligands in the same molecule were prepared by three different synthetic pathways. Compounds 1 a-d can be obtained by reaction of [{[CH(PPh2NSiMe3)2]LnCl2}2] with [K(thf)nN(PPh2)2] (n = 1.25, 1.5) or by treatment of [{(Ph2P)2N}LnCl2(thf)3] with K[CH(PPh2NSiMe3)2]. Furthermore, a one-pot reaction of K[CH(PPh2NSiMe3)2] with LnCl3 and [K(thf)nN(PPh2)2] leads to the same products. Single-crystal X-ray structures of 1 a-d show that the conformation of the six-membered metallacycle (N1-P1-C1-P2-N2-Ln) which is formed by chelation of the [CH(PPh2NSiMe3)2]- ligand to the lanthanide atom is influenced by the ionic radius of the central metal atom. In solution dynamic behavior of the [(Ph2P)2N]- ligand is observed, which is caused by rapid exchange of the two different phosphorus atoms. Further reaction of 1 b with KNPh2 resulted in [{(Me3SiNPPh2)2CH}La{N(PPh2)2}(NPh2)] (2). Compounds 1 a-d and 2 are active in the ring-opening polymerization of epsilon-caprolactone and the polymerization of methyl methacrylate. In some cases high molecular weight polymers with good conversions and narrow polydispersities were obtained. In both polymerizations the catalytic activity depends on the ionic radius of the metal center.     

Yttrium and lanthanide complexes having a chiral phosphanylamide in the coordination sphere

The chiral phosphanylamides {N(R-CHMePh)(PPh(2))}(-) and {N(S-CHMePh)(PPh(2))}(-) were introduced into rare earth chemistry. Transmetalation of the enantiomeric pure lithium compounds Li{N(R-CHMePh)(PPh(2))} (1a) and Li{N(S-CHMePh)(PPh(2))} (1b) with lanthanide bis(phosphinimino)methanide dichloride [{CH(PPh(2)NSiMe(3))(2)}LnCl(2)](2) in a 2:1 molar ratio in THF afforded the enantiomeric pure complexes [{CH(PPh(2)NSiMe(3))(2)}Ln(Cl){eta(2)-N(R-CHMePh)(PPh(2))}] (Ln = Er (2a), Yb (3a), Lu (4a)) and [{CH(PPh(2)NSiMe(3))(2)}Ln(Cl){eta(2)-N(S-CHMePh)(PPh(2))}] (Ln = Er (2b), Yb (3b), Lu (4b)). The solid-state structures of 2a and 3a,b were established by single-crystal X-ray diffraction. Attempts to synthesize compounds 3 in a one-pot reaction starting from K{CH(PPh(2)NSiMe(3))(2)}, YbCl(3), and 1 resulted in the lithium chloride incorporated complex [{(Me(3)SiNPPh(2))(2)CH}Yb(mu-Cl)(2)LiCl(THF)(2)] (5). In an alternative approach to give chiral rare earth compounds in a one-pot reaction 1a or 1b was reacted with LnCl(3) and K(2)C(8)H(8) to give the enantiomeric pure cyclooctatetraene compounds [{eta(2)-N(R-CHMePh)(PPh(2))}Ln(eta(8)-C(8)H(8))] (Ln = Y (6a), Er (7a), Yb (8)) and [{eta(2)-N(S-CHMePh)(PPh(2))}Ln(eta(8)-C(8)H(8))] (Ln = Y (6b), Er (7b)). The structures of 6a,b, 7a, and 8 were confirmed by single-crystal X-ray diffraction in the solid state.     

Synthesis and characterization of new biphenolate and binaphtholate rare-Earth-metal amido complexes: catalysts for asymmetric olefin hydroamination/cyclization

Monomeric diolate amido yttrium complexes [Y[diolate][N(SiHMe(2))(2)](thf)(2)] can be prepared in good yield by treating [Y[N(SiHMe(2))(2)](3)(thf)(2)] with either 3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diol (H(2)(Biphen)), 3,3'-bis(2,4,6-triisopropylphenyl)-2,2'-dihydroxy-1,1'-dinaphthyl (H(2)(Trip(2)BINO)) or 3,3'-bis(2,6-diisopropylphenyl)-2,2'-dihydroxy-1,1'-dinaphthyl (H(2)(Dip(2)BINO)) in racemic and enantiopure form. The racemic complex [Y(biphen)[N(SiHMe(2))(2)](thf)(2)] dimerizes upon heating to give the heterochiral complex (R,S)-[Y(biphen)[N(SiHMe(2))(2)](thf)](2). The corresponding dimeric heterochiral lanthanum complex was the sole product in the reaction of H(2)(Biphen) with [La[N(SiHMe(2))(2)](3)(thf)(2)]. Single-crystal X-ray diffraction of both dimeric complexes revealed that the two Ln(biphen)[N(SiHMe(2))(2)](thf) fragments are connected through bridging phenolate groups of the biphenolate ligands. The two different phenolate groups undergo an intramolecular exchange process in solution leading to their equivalence on the NMR timescale. All complexes were active catalysts for the hydroamination/cyclization of aminoalkynes and aminoalkenes at elevated temperature, with [Y((R)-dip(2)bino)[N(SiHMe(2))(2)](thf)(2)] being the most active one giving enantioselectivities of up to 57 % ee. Kinetic resolution of 2-aminohex-5-ene proceeded with this catalyst with 6.4:1 trans selectivity to give 2,5-dimethylpyrrolidine with a k(rel) of 2.6.     

Cationic ethylzinc compound: a benzene complex with catalytic activity in hydroamination and hydrosilylation reactions

The tight ion pair [EtZn(η(3)-C(6)H(6))][CHB(11)Cl(11)]·C(6)H(6) (1·C(6)H(6)) was obtained through β-hydrogen abstraction and concomitant ethene elimination from Et(2)Zn with the trityl salt [Ph(3)C][CHB(11)Cl(11)]. This ionlike species shows catalytic activity in hydrosilylation and intramolecular hydroamination reactions. The amine adduct {CH(2)CHCH(2)C(Ph(2))CH(2)NH(2)}(3)ZnCB(11)Cl(11) (3), which features a rare transition metal-carborane σ bond, was isolated from a hydroamination experiment.     

Synthesis, structures and reactions of lithium complexes of [(o-RCHC6H4)PPh2=NSiMe3]-(R = H, SiMe3) ligands

N-Trimethylsilyl o-methylphenyldiphenylphosphinimine, (o-MeC6H4)PPh2=NSiMe3 (1), was prepared by reaction of Ph2P(Br)=NSiMe3 with o-methylphenyllithium. Treatment of 1 with LiBun and then Me3SiCl afforded (o-Me3SiCH2C6H4)PPh2=NSiMe3 (2). Lithiations of both 1 and 2 with LiBu(n) in the presence of tmen gave crystalline lithium complexes [Li{CH(R)C6H4(PPh(2=NSiMe3)-.tmen](3, R = H; 4, R = SiMe3). From the mother liquor of 4, traces of the tmen-bridged complex [Li{CH(SiMe3)C6H4(PPh2=NSiMe3)-2}]2(mu-tmen) (5) were obtained. Reaction of 2 with LiBun in Et2O yielded complex [Li{CH(SiMe3)C6H4(PPh2=NSiMe3)-2}.OEt2] (6). Reaction of lithiated with Me2SiCl2 in a 2:1 molar ratio afforded dimethylsilyl-bridged compound Me2Si[CH2C6H4(PPh2=NSiMe3)-2]2 (7). Lithiation of 7 with two equivalents of LiBun in Et2O yielded [Li2{(CHC6H4(PPh2=NSiMe3)-2)2SiMe2}.0.5OEt2](8.0.5OEt2). Treatment of 4 with PhCN formed a lithium enamide complex [Li{N(SiMe3)C(Ph)CHC6H4(PPh2=NSiMe3)-2}.tmen] (9). Reaction of two equivalents of 5 with 1,4-dicyanobenzene gave a dilithium complex [{Li(OEt2)2}2(1,4-{C(N(SiMe3)CHC6H4(PPh2=NSiMe3)-2}2C6H4)] (10). All compounds were characterised by NMR spectroscopy and elemental analyses. The structures of compounds 2, 3, 5, 6 and 9 have been determined by single crystal X-ray diffraction techniques.     

Reactions of potassium bis(phosphinimino)methanide with group 11 compounds

Transmetalation of the potassium methanide complex, K{CH(PPh2NSiMe3)2}, with [(Ph3P)2CuI] afforded the corresponding copper complex [{CH(PPh2NSiMe3)2}CuPPh3] (1), whereas the reaction of K{CH(PPh2NSiMe3)2} with [Ph3PAuCl] resulted in the dinuclear gold complex [(Ph3PAu)2{C(PPh2NSiMe3)2}] (2). The solid-state structure of 1 shows the formation of a six-membered metallacycle (N1-P1-C1-P2-N2-Cu) that has a twist boat conformation. In contrast, compound 2 is an alpha,alpha-diaurated species, in which the two gold atoms are coordinated in a linear fashion onto the ligand backbone. Photoluminescence measurements show that the latter compound has a strong violet emission.     

A samarium cyclooctatetraene complex as catalyst for hydroamination/cyclisation catalysis

The cyclooctatetraene-bis(phosphinimino)methanide complex [[CH(PPh2NSiMe3)2]Sm(eta8-C8H8)] has been prepared; although this compound has no alkyl or amide ligand it shows moderate activity as a catalyst for the hydroamination/cyclisation reaction.     

Rare-earth metal complexes supported by 1,omega-dithiaalkanediyl-bridged bis(phenolato) ligands: synthesis, structure, and heteroselective ring-opening polymerization of rac-lactide

Monomeric yttrium and lutetium bis(phenolato) complexes [Ln(OSSO){N(SiHMe 2) 2}(THF)] (Ln = Y, Lu) were prepared from the reaction of silylamido complexes [Ln{N(SiHMe 2) 2} 3(THF) 2] with 1 equiv of tetradentate 1,omega-dithiaalkanediyl-bridged bis(phenol) (OSSO)H 2 1- 9 in moderate to high yields. In contrast to the rigid configuration of scandium analogues, the yttrium complexes 2b and 3b and the lutetium complex 3c that contain a C 2 bridge between the two sulfur donors of the ligand are symmetric in solution. The monomeric nature of these complexes was indicated by an X-ray diffraction study of the yttrium complex 6b. The yttrium center in 6b is coordinated to the tetradentate [OSSO]-type ligand, one silylamido group and one THF ligand with the two oxygen donors of the [OSSO]-type ligand located trans. Corresponding bis(phenolato) silylamido complexes of larger rare-earth metals could not be obtained from similar reactions: Reaction of [La{N(SiHMe 2) 2} 3(THF) 2] with 1,2-xylylene-linked bis(phenol) gave a dinuclear lanthanum complex 6d of the formula [La 2(OSSO) 3] with two inequivalent eight-coordinate metal centers. The yttrium and lutetium complexes efficiently initiated the ring-opening polymerization (ROP) of lactides in THF. The heteroselectivity during the ROP of rac-lactide was enhanced when the steric demand of the bis(phenolato) ligand was increased, either by extending the bridge length or by introducing bulky ortho-substituents in the phenoxy units. A C 3 bridge within the ligand backbone is essential to allow configurational interconversion of the active site between Lambda and Delta configuration during polymerization, allowing accommodation of both enantiomers of the monomer in an alternating fashion.     

Synthesis, structure and hydrosilylation activity of neutral and cationic rare-earth metal silanolate complexes

Rare-earth metal alkyl tri(tert-butoxy)silanolate complexes [Ln{mu,eta2-OSi(O(t)Bu)3}(CH2SiMe3)2]2 (Ln = Y (1), Tb (2), Lu (3)) were prepared via protonolysis of the appropriate tris(alkyl) complex [Ln(CH2SiMe3)3(thf)2] with tri(tert-butoxy)silanol in pentane. Crystal structure analysis revealed a dinuclear structure for with square pyramidal geometry at the yttrium centre. The silanolate ligand coordinates in an eta2-bridging coordination mode giving a 4-rung truncated ladder and non-crystallographic inversion centre. Addition of two equiv. of 12-crown-4 to a pentane solution of 1 or 3 respectively gave [Ln{OSi(O(t)Bu)(3)}(CH2SiMe3)2(12-crown-4)].12-crown-4 (Ln = Y (4), Lu (5)). Crystal structure analysis of 5 showed a slightly distorted octahedral geometry at the lutetium centre. The silanolate ligand adopts an eta(1)-terminal coordination mode, whilst the crown ether unit coordinates in an unusual kappa3-fashion. Reaction of 1-3 with [NEt3H]+[BPh4]- in thf yielded the cationic derivatives [Ln{OSi(O(t)Bu)3}(CH2SiMe3)(thf)4]+[BPh4]- (Ln = Y (6), Tb (7) and Lu (8)); coordination of crown ether led to compounds of the form [Ln{OSi(O(t)Bu)3}(CH2SiMe3)(L)(thf)n]+[BPh4]- (Ln = Y, Lu, L = 12-crown-4, n = 1 (9,10); Ln = Y, Lu, L = 15-crown-5, n = 0 (11,12)). Reaction of 1 with [NMe2PhH]+[B(C6F5)4]-, [Al(CH2SiMe3)3] or BPh3 in thf gave the ion pairs [Y{OSi(O(t)Bu)3}(CH2SiMe3)(thf)4]+[A]- ([A]- = [B(C6F5)4]- (13), [Al(CH2SiMe3)4]- (14), [BPh3(CH2SiMe3)]- (15)), whilst two equiv. [NMe2PhH]+[BPh4]- with 1 in thf produced the dicationic ion triple [Y{OSi(O(t)Bu)3}(thf)6]2+[BPh4]-2 (16). Crystal structure analysis revealed that 16 is mononuclear with pentagonal bipyramidal geometry at the yttrium centre. The silanolate ligand coordinates in an eta(1)-terminal fashion. All diamagnetic compounds have been characterized by NMR spectroscopy. 1, 3, 4, 6 and 13 were tested as olefin hydrosilylation pre-catalysts with a variety of substrates; 1 was found to be highly active in 1-decene hydrosilylation.     

Synthesis of amidolanthanides with new chiral biaryl-based NNO ligands and their use as catalysts for enantioselective hydroamination/cyclization

A new series of amidolanthanides have been prepared from the reactions between Ln[N(SiMe3)2]3 and the chiral NNO ligands, (S)-2-(pyrrol-2-ylmethyleneamino)-2'-hydroxy-6,6'-dimethyl-1,1'-biphenyl (2H2) and (S)-5,5',6,6',7,7',8,8'-octahydro-2-(pyrrol-2-ylmethyleneamino)-2'-hydroxy-1,1'-binaphthyl (3H2), which are synthesized from the condensation of pyrrole-2-carboxaldehyde with 1 equiv of (S)-2-amino-2'-hydroxy-6,6'-dimethyl-1,1'-biphenyl or (S)-5,5',6,6',7,7',8,8'-octahydro-2-amino-2'-hydroxy-1,1'-binaphthyl, in the presence of molecular sieves at 70 degrees C, respectively. Treatment of 2H2 with 1 equiv of Ln[N(SiMe3)2]3 (Ln=Sm, Yb) in toluene under reflux, followed by recrystallization from a toluene solution, gives the dimeric amido complexes, {2-SmN(SiMe3)2}2.0.5C7H8 (6.0.5C7H8) and {2-YbN(SiMe3)2} 2.1.5C7H8(8.1.5C7H8), in good yields. While under similar reaction conditions, the reaction of 2H2 with 1 equiv of Y[N(SiMe3)2]3 leads to the isolation of a mixture of {2-YN(SiMe3)2}2 (7a) and {(2)2Y}Y[N(SiMe3)2]2(7b) in 82% total yield; the reaction of 3H2 with 1 equiv of Ln[N(SiMe3)2]3 (Ln=Y, Yb) gives the trinuclear complexes, {(3)2Ln}2LnN(SiMe3) 2.1.5C7H8 (Ln=Y(9.1.5C7H8), Yb(10.1.5C7H8)), in good yields. All compounds have been characterized by various spectroscopic techniques and elemental analyses. The solid-state structures of compounds 2H2 and 6- 10 have been further confirmed by X-ray diffraction analyses. Complexes 6- 9 are active catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in good yields with moderate ee values.     

Scandium alkyl and amide complexes containing a cyclen-derived (NNNN) macrocyclic ligand: synthesis, structure and ring-opening polymerization activity toward lactide monomers

Cyclic polyamine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane, (Me(3)TACD)H (= Me(3)[12]aneN(4)), reacted with [K{N(SiHMe(2))(2)}] in benzene-d(6) to give [K{(Me(3)TACD)SiMe(2)N(SiHMe(2))}] (1) under hydrogen evolution. Single-crystal X-ray diffraction of 1 shows a dinuclear structure in the solid state, featuring a bridging μ-amido and a weak β-agostic Si-H bond. 1,7-Dimethyl-1,4,7,10-tetraazacyclododecane (Me(2)TACD)H(2) (= Me(2)[12]aneN(4)) and (Me(3)TACD)H were reacted with [Sc{N(SiHMe(2))(2)}(3)(thf)] in benzene-d(6) to give [{(Me(2)TACD)SiMe(2)N(SiHMe(2))}Sc{N(SiHMe(2))(2)}] (2) and [(Me(3)TACD)Sc{N(SiHMe(2))(2)}(2)SiMe(2)] (3), respectively. Both compounds are monomeric in solution and X-ray diffraction studies showed the scandium metal centers to be six-coordinate. The scandium alkyl complex [Sc(Me(3)TACD)(CH(2)SiMe(3))(2)] (4) was obtained by reacting (Me(3)TACD)H with [Sc(CH(2)SiMe(3))(3)(thf)] in benzene-d(6). The scandium amide complexes 2 and 3 catalyzed the ring-opening polymerization (ROP) of meso-lactide to give syndiotactic polylactides.     

C2-symmetric bis(oxazolinato)lanthanide catalysts for enantioselective intramolecular hydroamination/cyclization

C(2)-symmetric bis(oxazolinato)lanthanide complexes of the type [(4R,5S)-Ph(2)Box]La[N(TMS)(2)](2), [(4S,5R)-Ar(2)Box]La[N(TMS)(2)](2), and [(4S)-Ph-5,5-Me(2)Box]La[N(TMS)(2)](2) (Box = 2,2'-bis(2-oxazoline)methylenyl; Ar = 4-tert-butylphenyl, 1-naphthyl; TMS = SiMe(3)) serve as precatalysts for the efficient enantioselective intramolecular hydroamination/cyclization of aminoalkenes and aminodienes. These new catalyst systems are conveniently generated in situ from the known metal precursors Ln[N(TMS)(2)](3) or Ln[CH(TMS)(2)](3) (Ln = La, Nd, Sm, Y, Lu) and 1.2 equiv of commercially available or readily prepared bis(oxazoline) ligands such as (4R,5S)-Ph(2)BoxH, (4S,5R)-Ar(2)BoxH, and (4S)-Ph-5,5-Me(2)BoxH. The X-ray crystal structure of [(4S)-(t)BuBox]Lu[CH(TMS)(2)](2) provides insight into the structure of the in situ generated precatalyst species. Lanthanides having the largest ionic radii exhibit the highest turnover frequencies as well as enantioselectivities. Reaction rates maximize near 1:1 BoxH:Ln ratio (ligand acceleration); however, increasing the ratio to 2:1 BoxH:Ln decreases the reaction rate, while affording enantiomeric excesses similar to the 1:1 BoxH:Ln case. A screening study of bis(oxazoline) ligands reveals that aryl stereodirecting groups at the oxazoline ring 4 position and additional substitution (geminal dimethyl or aryl) at the 5 position are crucial for high turnover frequencies and good enantioselectivities. The optimized precatalyst, in situ generated [(4R,5S)-Ph(2)Box]La[N(TMS)(2)](2), exhibits good rates and enantioselectivities, comparable to or greater than those achieved with chiral C(1)-symmetric organolanthanocene catalysts, even for poorly responsive substrates (up to 67% ee at 23 degrees C). Kinetic studies reveal that hydroamination rates are zero order in [amine substrate] and first order in [catalyst], implicating the same general mechanism for organolanthanide-catalyzed hydroamination/cyclizations (intramolecular turnover-limiting olefin insertion followed by the rapid protonolysis of an Ln-C bond by amine substrate) and implying that the active catalytic species is monomeric.     

High tetraalkylaluminate fluxionality in half-sandwich complexes of the trivalent rare-earth metals

Steric factors govern the formation of half-sandwich complexes (C5Me4R)Ln[N(SiHMe2)2]2 according to acid-base reactions utilising Ln[N(SiHMe2)2)3(thf)2 and substituted cyclopentadienes. Subsequent trimethylaluminium-promoted silylamide elimination produces the first half-sandwich bis(tetramethylaluminate) complexes (C5Me4R)Ln(AlMe4)2.     

Rhenium(V) and technetium(V) complexes with phosphoraneimine and phosphoraneiminato ligands

Air-stable rhenium(V) nitrido complexes are formed when [ReOCl3(PPh3)2], [NBu4][ReOCl4], or [NBu4][ReNCl4] are treated with an excess of silylated phosphoraneiminates of the composition Me3SiNPPh3 or Ph2P(NSiMe3)CH2PPh2 in CH2Cl2. Complexes of the compositions [ReNCl(Ph2PCH2PPh2NH)2]Cl (1), [ReN(OSiMe3)(Ph2PCH2PPh2NH)2]Cl (2) or [ReNCl2(PPh3)2] (3) were isolated and structurally characterized. The latter compound was also produced during a reaction of the rhenium(III) precursor [ReCl3(PPh3)2(CH3CN)] and Me3SiNPPh3. Nitrogen transfer from the phosphorus to the rhenium atoms and the formation of nitrido ligands were observed in all examples. All products of reactions with an excess of the potentially chelating phosphoraneiminate Me3SiNP(Ph2)CH2PPh2 contain neutral Ph2PCH2PPh2NH ligands. The required protons are supplied by a metal-induced decomposition of the solvent dichloromethane. The Re-N(imine) bond lengths (2.055-2.110 A) indicate single bonds, whereas the N-P bond with lengths between 1.596 A and 1.611 A reflect considerable double bond character. An oxorhenium(V) phosphoraneiminato complex, the dimeric compound [ReOCl2(mu-N-Ph2PCH2PPh2N)]2 (4), is formed during the reaction of [NBu4][ReOCl4] with an equivalent amount of Ph2P(NSiMe3)CH2PPh in dry acetonitrile. The blue neutral complex with two bridging phosphoraneiminato units is stable as a solid and in dry solvents. It decomposes in solution, when traces of water are present. The rhenium-nitrogen distances of 2.028(3) and 2.082(3) A are in the typical range of bridging phosphoraneiminates and an almost symmetric bonding mode. Technetium complexes with phosphoraneimine ligands were isolated from reactions of [NBu4][TcOCl4] with Me3SiNPPh3, and [NBu4][TcNCl4] with Me3SiNP(Ph2)CH2PPh2. Nitrogen transfer and the formation of a five-coordinate nitrido species, [TcNCl2(HNPPh3)2] (5), was observed in the case of the oxo precursor, whereas reduction of the technetium(VI) starting material and the formation of the neutral technetium(V) complex [TcNCl2(Ph2PCH2PPh2NH)] (6) or [TcNCl(Ph2PCH2PPh2NH)2]Cl (7) was observed in the latter case. Both technetium complexes are air stable and X-ray structure determinations show bonding modes of the phosphoraneimines similar to those in the rhenium complexes.     

Lanthanide-potassium wheels

Mixed potassium-lanthanide wheel-shaped-structured, hexanuclear coordination oligomers of composition [(eta5-C5H5)Ln(NPh2)2{N(PPh2)2}2K2(THF)4]2 (Ln = Er (1a), Yb (1b)) and an octanuclear coordination polymer of composition [(eta5-C5H5)Sm(NPh2)2{N(PPh2)2}K]infinity (2) were synthesized. All presented compounds can be obtained in moderate yields in a one-pot procedure, in which the potassium salts KNPh2 and [K(THF)(n)N(PPh2)2] as well as NaC5H5 are reacted with anhydrous samarium, erbium, and ytterbium trichloride in THF.     

Controlled syntheses, characterization, and reactivity of neutral and anionic lanthanide amides supported by methylene-linked bis(phenolate) ligands

A series of neutral and anionic bis(phenolate) lanthanide amides were synthesized by general metathesis reactions, and their reactivity was explored. Protolytic ligand exchange reactions of MBMPH2 (MBMP = 2,2'-methylene bis(6-tert-butyl-4-methyl-phenolate)) with [Ln{N(TMS)2}2(mu-Cl)(THF)]2 (TMS = SiMe3) afforded the desired bridged bis(phenolate) lanthanide chlorides [(MBMP)Ln(mu-Cl)(THF)2]2 [Ln = Nd (1), Yb (2)] in high isolated yields. These lanthanide chlorides were found to be useful precursors for the synthesis of the corresponding lanthanide derivatives. Reactions of 1 and 2 with 2 equiv of NaN(TMS)2 in THF produced the expected neutral bis(phenolate) lanthanide amido complexes (MBMP)Ln[N(TMS)2](THF)2 [Ln = Nd (3), Yb (4)] in high yields. Whereas the reactions of 1 and 2 with LiN(TMS)2 in a 1:4 molar ratio gave the anionic bis(phenolate) lanthanide amides as discrete ion-pair complexes [Li(THF)4][(MBMP)Ln{N(TMS)2}2] [Ln = Nd (5), Yb (6)] in high isolated yields. Further study revealed that 5 and 6 can also be conveniently synthesized in high yields by the direct reactions of MBMPH2 with [Ln{N(TMS)2}2(mu-Cl)(THF)]2 in a 2:1 molar ratio, and then with 4 equiv of nBuLi. The reactivity of the neutral and anionic bis(phenolate) lanthanide amides was comparatively investigated. It was found that the insertion reactions of carbodiimide into the Ln-N bond of neutral lanthanide amido complexes 3 and 4 gave the anticipated bis(phenolate) lanthanide guanidinate complexes [(mu-O-MBMP)Nd{(iPrN)2CN(TMS)2}]2 (7) and (MBMP)Yb[(iPrN)2CN(TMS)2] (8), respectively, in high yields, whereas the similar reaction of carbodiimide with anionic amido complex 5 provided the unexpected ligand-redistributed products, and the homoleptic ion-pair bis(phenolate) neodymium complex [Li(DME)2(THF)][(MBMP)2Nd(THF)2] (9) was finally isolated as one of the products. Furthermore, the anionic bis(phenolate) lanthanide amides showed higher catalytic activity for the polymerization of epsilon-caprolactone than the neutral ones. All of the complexes were characterized with elemental analysis and IR spectra, and the definitive molecular structures of 1-3 and 5-9 were provided by single-crystal X-ray analyses.     

Steric control over the formation of cis and trans bis-chelated palladium(II) complexes using a new series of flexible N,P pyridyl-phosphine ligands

The deprotection of phosphonium chloride salts [PR2(CH2OH)2]+Cl- and subsequent condensation reaction with N-methyl-2-aminopyridine has been carried out to give a series of ligands of the form PR2CH2N(CH3)C5H4N (R=Ph , Cy , t-Bu ) which have been fully characterised either as the pure ligand () or the air stable borane adducts (R=Cy , t-Bu ). The 1:1 reactions of , and with PdCl2(COD) gave the N,P chelate complexes [Pd{PR2CH2N(CH3)C5H4N}Cl2]; the Cy () and t-Bu () complexes were characterised by X-ray crystallography. The bisligated species [Pd{PCy2CH2N(CH3)C5H4N}2Cl2] () was obtained when the reaction was carried out at higher temperatures and the ligands were found to be coordinated to the metal in a trans configuration through the phosphorus donors. Abstraction of the chlorides from the bis-ligated species , using silver salts, resulted in the coordination of the pyridine ring forming the bis-chelate complex [Pd{PCy2CH2N(CH3)C5H4N}2]2+. In comparison, the palladium bis-chelate complex of ligand [Pd{PPh2CH2N(CH3)C5H4N}2]2+ () was shown to form in a cis configuration and was fully characterised by X-ray crystallography.     

Heavier alkaline earth catalysts for the intermolecular hydroamination of vinylarenes, dienes, and alkynes

The heavier group 2 complexes [M{N(SiMe(3))(2)}(2)](2)(1, M = Ca; 2, M = Sr) and [M{CH(SiMe(3))(2)}(2)(THF)(2)] (3, M = Ca; 4, M = Sr) are shown to be effective precatalysts for the intermolecular hydroamination of vinyl arenes and dienes under mild conditions. Initial studies revealed that the amide precatalysts, 1 and 2, while compromised in terms of absolute activity by a tendency toward transaminative behavior, offer greater stability toward polymerization/oligomerization side reactions. In every case the strontium species, 2 and 4, were found to outperform their calcium congeners. Reactions of piperidine with para-substituted styrenes are indicative of rate-determining alkene insertion in the catalytic cycle while the ease of addition of secondary cyclic amines was found to be dependent on ring size and reasoned to be a consequence of varying amine nucleophilicity. Hydroamination of conjugated dienes yielded isomeric products via η(3)-allyl intermediates and their relative distributions were explained through stereoelectronic considerations. The ability to carry out the hydroamination of internal alkynes was found to be dramatically dependent upon the identity of the alkyne substituents while reactions employing terminal alkynes resulted in the precipitation of insoluble and unreactive group 2 acetylides. The rate law for styrene hydroamination with piperidine catalyzed by [Sr{N(SiMe(3))(2)}(2)](2) was deduced to be first order in [amine] and [alkene] and second order in [catalyst], while large kinetic isotope effects and group 2 element-dependent ΔS(++) values implicated the formation of an amine-assisted rate-determining alkene insertion transition state in which there is a considerable entropic advantage associated with use of the larger strontium center.     

Triazenide complexes of the heavier alkaline earths: synthesis, characterization, and suitability for hydroamination catalysis

A series of triazenide complexes of the heavier alkaline earths, Ca, Sr and Ba, have been synthesized by either protonolysis or salt metathesis routes. Although complexes of the form [{Ar 2N 3}M{N(SiMe 3) 2}(THF) n ] (M = Ca, n = 2; M = Sr, n = 3; Ar = 2,6-diisopropylphenyl) and [{Ar 2N 3}Ca(I)(THF) 2] 2 could be isolated and characterized by X-ray crystallography, solution studies revealed the propensity of these species to undergo Schlenk-like redistribution with the formation of [{Ar 2N 3} 2M(THF) n ] (M = Ca, n = 1; M = Sr, n = 2). The latter compounds have been synthesized independently. In the case of the large barium dication, attempts to synthesize the heaviest analogue of the series, [{Ar 2N 3} 2Ba(THF) n ], failed and led instead to the isolation of the potassium barate complex [K{Ar 2N 3}Ba{N(SiMe 3) 2} 2(THF) 4]. Single crystal X-ray diffraction studies demonstrated that, although in all the aforementioned cases the triazenide ligand binds to the electrophilic group 2 metal centers via symmetrical kappa (2)- N, N-chelates, in the latter compound an unprecedented bridging mode is observed in which the triazenide ligand coordinates through both terminal and internal nitrogen centers. A series of density-functional theory computational experiments have been undertaken to assist in our understanding of this phenomenon. In further experiments, the calcium and strontium amide derivatives [{Ar 2N 3}M{N(SiMe 3) 2}(THF) n ] (M = Ca, n = 2; M = Sr, n = 3) proved to be catalytically active for the intramolecular hydroamination of 1-amino-2,2-diphenylpent-4-ene to form 2-methyl-4,4-diphenylpyrrolidine, with the calcium species demonstrating a higher turnover number than the strontium analogue ( 2a, TOF = 500 h (-1); 2b, TOF = 75 h (-1)). In these instances, because of ambiguities in the structural charcterization of the precatalyst in solution, such quantification holds little value and detailed catalytic studies have not been conducted.