Ni(II) and Fe(II) complexes based on bis(imino)aryl pincer ligands: synthesis, structural characterization and catalytic activities

Bis(imino)aryl NCN pincer Ni(II) complexes 2,6-(ArN=CH)(2)C(6)H(3)NiBr (1: Ar = 2,6-Me(2)C(6)H(3); 2: Ar = 2,6-Et(2)C(6)H(3); 3: Ar = 2,6-(i)Pr(2)C(6)H(3)) were prepared via the oxidative-addition of Ni(0)(Ph(3)P)(4) with bis(N-aryl)-2-bromoisophthalaldimine. These nickel complexes were characterized by NMR and elemental analyses. Their solid molecular structures were established by X-ray diffraction analyses. The nickel metal centers adopt distorted square planar geometries with the bromine atoms acting as one coordinate ligands. The NCN pincer Fe(II) complexes 2,6-(ArN=CH)(2)C(6)H(3)Fe(μ-Cl)(2)Li(THF)(2) (4: Ar = 2,6-Me(2)C(6)H(3); 5: Ar = 2,6-Et(2)C(6)H(3); 6: Ar = 2,6-(i)Pr(2)C(6)H(3)) were synthesized by lithium salt metathesis reactions of the ligand lithium salts with FeCl(2). X-ray structure analyses of 4 and 5 revealed that the Fe(II) complexes are hetero-dinuclear with the iron atoms in trigonal bipyramidal environments. When activated with MAO, the nickel complexes are active for norbornene vinyl polymerization but are inert for butadiene polymerization. The Fe(II) complexes show moderate activities in butadiene polymerization when activated with alkylaluminium, affording the cis-1,4 enriched polymer.     

Two-coordinate, quasi-two-coordinate, and distorted three coordinate, T-shaped chromium(II) amido complexes: unusual effects of coordination geometry on the lowering of ground state magnetic moments

The synthesis and characterization of the mononuclear chromium(II) terphenyl substituted primary amido-complexes Cr{N(H)Ar(Pr(i)(6))}(2) (Ar(Pr(i)(6)) = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-(i)Pr(3))(2) (1), Cr{N(H)Ar(Pr(i)(4))}(2) (Ar(Pr(i)(4)) = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2) (2), Cr{N(H)Ar(Me(6))}(2) (Ar(Me(6)) = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Me(3))(2) (4), and the Lewis base adduct Cr{N(H)Ar(Me(6))}(2)(THF) (3) are described. Reaction of the terphenyl primary amido lithium derivatives Li{N(H)Ar(Pr(i)(6))} and Li{N(H)Ar(Pr(i)(4))} with CrCl(2)(THF)(2) in a 2:1 ratio afforded complexes 1 and 2, which are extremely rare examples of two coordinate chromium and the first stable chromium amides to have linear coordinated high-spin Cr(2+). The reaction of the less crowded terphenyl primary amido lithium salt Li{N(H)Ar(Me(6))} with CrCl(2)(THF)(2) gave the tetrahydrofuran (THF) complex 3, which has a distorted T-shaped metal coordination. Desolvation of 3 at about 70 °C gave 4 which has a formally two-coordinate chromous ion with a very strongly bent core geometry (N-Cr-N= 121.49(13)°) with secondary Cr--C(aryl ring) interactions of 2.338(4) ? to the ligand. Magnetometry studies showed that the two linear chromium species 1 and 2 have ambient temperature magnetic moments of about 4.20 μ(B) and 4.33 μ(B) which are lower than the spin-only value of 4.90 μ(B) typically observed for six coordinate Cr(2+). The bent complex 4 has a similar room temperature magnetic moment of about 4.36 μ(B). These studies suggest that the two-coordinate chromium complexes have significant spin-orbit coupling effects which lead to moments lower than the spin only value of 4.90 μ(B) because λ (the spin orbit coupling parameter) is positive. The three-coordinated complex 3 had a magnetic moment of 3.79 μ(B).     

New titanium complexes with symmetric or asymmetric cis-9,10-dihydrophenanthrenediamide ligands formed through sequential intramolecular C-C bond-forming reactions

A series of new titanium(IV) complexes with symmetric or asymmetric cis-9,10-dihydrophenanthrenediamide ligands, cis-9,10-PhenH(2)(NR)(2)Ti(O(i)Pr)(2) [PhenH(2) = 9,10-dihydrophenanthrene, R = 2,6-(i)Pr(2)C(6)H(3) (2a), 2,6-Et(2)C(6)H(3) (2b), 2,6-Me(2)C(6)H(3) (2c)], cis-9,10-PhenH(2)(NR(1))(NR(2))Ti(O(i)Pr)(2) [R(1) = 2,6-(i)Pr(2)C(6)H(3), R(2) = 2,6-Et(2)C(6)H(3) (2d); R(1) = 2,6-(i)Pr(2)C(6)H(3), R(2) = 2,6-Me(2)C(6)H(3) (2e)], and [cis-9,10-PhenH(2)(NR(1))(2)][o-C(6)H(4)(CH=NR(2))]TiO(i)Pr [R(1) = 2,6-(i)Pr(2)C(6)H(3), R(2) = 2,6-Et(2)C(6)H(3) (3a); R(1) = 2,6-(i)Pr(2)C(6)H(3), 2,6-Me(2)C(6)H(3) (3b)], have been synthesized from the reactions of TiCl(2)(O(i)Pr)(2) with o-C(6)H(4)(CH=NR)Li [R = 2,6-(i)Pr(2)C(6)H(3), 2,6-Et(2)C(6)H(3), 2,6-Me(2)C(6)H(3)]. The symmetric complexes 2a-2c were obtained from the reactions of TiCl(2)(O(i)Pr)(2) with 2 equiv of the corresponding o-C(6)H(4)(CH=NR)Li followed by intramolecular C-C bond-forming reductive elimination and oxidative coupling processes, while the asymmetric complexes 2d-2e were formed from the reaction of TiCl(2)(O(i)Pr)(2) with two different types of o-C(6)H(4)(CH=NR)Li sequentially. The complexes 3a and 3b were also isolated from the reactions for complexes 2d and 2e. All complexes were characterized by (1)H and (13)C NMR spectroscopy, and the molecular structures of 2a, 2b, 2e, and 3a were determined by X-ray crystallography.     

Al and Zn complexes bearing N,N,N-tridentate quinolinyl anilido-imine ligands: synthesis, characterization and catalysis in l-lactide polymerization

Reactions of N,N,N-tridentate quinolinyl anilido-imine ligands with AlMe(3) afford mononuclear aluminum complexes {κ(3)-[{2-[ArN[double bond, length as m-dash]C(H)]C(6)H(4)}N(8-C(9)H(6)N)]}AlMe(2) (Ar = 2,6-Me(2)C(6)H(3) (1a), 2,6-Et(2)C(6)H(3) (1b), 2,6-(i)Pr(2)C(6)H(3) (1c)) or dinuclear complexes AlMe(3){κ(1)-[{2-[ArN[double bond, length as m-dash]C(H)C(6)H(4)]N(8-C(9)H(6)N)}-κ(2)]AlMe(2) (R = 2,6-Me(2)C(6)H(3) (2a), 2,6-Et(2)C(6)H(3) (2b), 2,6-(i)Pr(2)C(6)H(3) (2c)) depending on the ratios of reactants used. Similar reactions of ZnEt(2) with these ligands give the monoligated ethyl zinc complexes {κ(3)-[{2-[ArN[double bond, length as m-dash]C(H)]C(6)H(4)}N(8-C(9)H(6)N)]}ZnEt (Ar = 2,6-Me(2)C(6)H(3) (3a), 2,6-Et(2)C(6)H(3) (3b), 2,6-(i)Pr(2)C(6)H(3) (3c)) or bisligated complexes {κ(3)-[{2-[ArN[double bond, length as m-dash]C(H)]C(6)H(4)}N(8-C(9)H(6)N)]}Zn{κ(2)-[{2-[ArN[double bond, length as m-dash]C(H)]C(6)H(4)}N(8-C(9)H(6)N)]} (Ar = 2,6-Me(2)C(6)H(3) (4a), 2,6-Et(2)C(6)H(3) (4b), 2,6-(i)Pr(2)C(6)H(3) (4c)). These complexes were well characterized by NMR and the structures of 1a, 2a, 2c, 3b and 4c were confirmed by X-ray diffraction analysis. The aluminum and zinc complexes were tested to initiate lactide polymerization in which the zinc complexes show moderate to high activities in the presence of benzyl alcohol.     

Activation of carbodiimide and transformation with amine to guanidinate group by Ln(OAr)3(THF)2 (Ln: lanthanide and yttrium) and Ln(OAr)3(THF)2 as a novel precatalyst for addition of amines to carbodiimides: influence of aryloxide group

Reaction of Ln(OAr(1))(3)(THF)(2) (Ar(1)= [2,6-((t)Bu)(2)-4-MeC(6)H(2)] with carbodiimides (RNCNR) in toluene afforded the RNCNR coordinated complexes (Ar(1)O)(3)Ln(NCNR) (R = (i)Pr (isopropyl), Ln = Y (1) and Yb (2); R = Cy (cyclohexyl), Ln = Y (3)) in high yields. Treatment of 1 and 2 with 4-chloroaniline, respectively, at a molar ratio of 1:1 yielded the corresponding monoguanidinate complex (Ar(1)O)(2)Y[(4-Cl-C(6)H(4)N)C(NH(i)Pr)N(i)Pr](THF) (4) and (Ar(1)O)(2)Yb[(4-Cl-C(6)H(4)N)C(NH(i)Pr)N(i)Pr](THF) (5). Complexes 4 and 5 can be prepared by the reaction of Ln(OAr(1))(3)(THF)(2) with RNCNR and amine in toluene at a 1:1:1 molar ratio in high yield directly. A remarkable influence of the aryloxide ligand on this transformation was observed. The similar transformation using the less bulky yttrium complexes Y(OAr(2))(3)(THF)(2) (Ar(2) = [2,6-((i)Pr)(2)C(6)H(3)]) or Y(OAr(3))(3)(THF)(2) (Ar(3) = [2,6-Me(2)C(6)H(3)]) did not occur. Complexes Ln(OAr(1))(3)(THF)(2) were found to be the novel precatalysts for addition of RNCNR with amines, which represents the first example of catalytic guanylation by the lanthanide complexes with the Ln-O active group. The catalytic activity of Y(OAr(1))(3)(THF)(2) was found to be the same as that of monoguanidinate complex 4, indicating 4 is one of the active intermediates in the present process. The other intermediate, amide complex (Ar(1)O)(2)Ln[(2-OCH(3)-C(6)H(4)NH)(2-OCH(3)-C(6)H(4)NH(2))] (6), was isolated by protonolysis of 4 with 2-OCH(3)-C(6)H(4)NH(2). All the complexes were structurally characterized by X-ray single crystal determination.     

The role of neutral coligands on the stabilization of mono-Tp(i)Pr2 U(III) complexes

The reaction of [UI(3)(THF)(4)] with 1 equiv of KTp()i(Pr)()2 in toluene in the presence of several neutral coligands allowed the synthesis of a novel family of mono-Tp()i(Pr)()2 complexes, [UI(2)Tp()i(Pr)()2(L)(x)()] [L = OPPh(3), x = 1 (3); L = C(5)H(5)N, x = 2 (4); L = Hpz()t(Bu,Me), x = 2 (5); and L = bipy, x = 1 (6)]. The adduct with THF, [UI(2)Tp()i(Pr)()2(THF)(2)(-)(3)] (1), could also be isolated by reacting [UI(3)(THF)(4)] with 1 equiv of KTp()i(Pr)()2 in tetrahydrofuran. However, complex 1 is not a good starting material to enter into the mono-Tp()i(Pr)()2 U(III) complexes as it decomposes in solution, leading to mixtures of U(III) species coordinated with Hpz()i(Pr)()2. The solid-state structures of 3, 4, and 6 were determined by single-crystal X-ray diffraction and revealed that this family of mono-Tp()i(Pr)()2 complexes can be six- (3) or seven-coordinated (4 and 6), depending on the nature of the neutral coligand. Complex 3 displays distorted octahedral coordination geometry, while 4 and 6 display distorted pentagonal bipyramid and capped octahedral geometries, respectively. Complexes 3 and 6 are static in solution, and the patterns of the (1)H NMR spectra are consistent with the C(s)() symmetry found in the solid state. The other complexes (1, 4, and 5) are fluxional, but the dynamic processes involved can be slowed by decreasing the temperature.     

Utility of Arylamido Ligands in Yttrium and Lanthanide Chemistry(1)

The reactivity of KNHAr reagents (Ar = C(6)H(5), C(6)H(3)Me(2)-2,6, C(6)H(3)(i)Pr(2)-2,6) with lanthanide and yttrium trichlorides has been investigated. With the larger metals Nd and Sm and the smaller 2,6-dimethyl-substituted ligand, the bimetallic dianionic complexes [K(THF)(6)](2)[Ln(&mgr;-NHC(6)H(3)Me(2)-2,6)(NHC(6)H(3)Me(2)-2,6)(3)](2) (Ln: Sm, 1a; Nd, 1b) are isolated as the potassium salts. Under the same reaction conditions YCl(3) forms a bimetallic anion which retains chloride: [K(DME)(2)(THF)(3)][Y(2)(&mgr;-NHC(6)H(3)Me(2)-2,6)(2)(&mgr;-Cl)(NHC(6)H(3)Me(2)-2,6)(4)(THF)(2)], 2. With the larger 2,6-diisopropyl ligands, neutral complexes are isolated in both solvated monometallic and unsolvated bimetallic forms. With Nd, a distorted octahedral trisolvate, Nd(NHC(6)H(3)(i)Pr(2)-2,6)(3)(THF)(3), 3, was obtained, whereas with Yb and Y the trigonal bipyramidal disolvates, Ln(NHC(6)H(3)(i)Pr(2)-2,6)(3)(THF)(2) (Ln: Yb, 4a; Y, 4b), were isolated. THF-free complexes of the NHC(6)H(3)(i)Pr(2)-2,6 ligand are available by reacting the amine NH(2)C(6)H(3)(i)Pr(2)-2,6 with Ln[N(SiMe(3))(2)](3) complexes. By this route, the dimers [Ln(&mgr;-NHC(6)H(3)(i)Pr(2)-2,6)(NHC(6)H(3)(i)Pr(2)-2,6)(2)](2) (Ln: Yb, 5a; Y, 5b) were isolated. The reaction of the unsubstituted arylamido salt KNHC(6)H(5) with NdCl(3) produced an insoluble material which was characterized as [Nd(NHC(6)H(5))(3)(KCl)(3)], 6. 6 reacted with Al(2)Me(6) in hexanes and produced a heteroleptic mixed-metal complex {[Me(2)Al(&mgr;-Me(2))](2)Nd(&mgr;(3)-NC(6)H(5))(&mgr;-Me)AlMe}(2), 7, and the trimeric aluminum arylamido complex [Me(2)Al(&mgr;-NHC(6)H(5))](3), 8. The solvent of crystallization and relevant crystallographic data for the compounds identified by X-ray analysis follow: 1a,THF, 156 K, P2(1)/n, a = 12.985(2) ?, b = 27.122(5) ?, c = 17.935(3) ?, beta = 100.19(1) degrees, V = 6216(1) ?(3), Z = 2, 6148 reflections (I > 3sigma(I)), R(F)() = 7.1%; 1b,THF, 156 K, P2(1)/n, a = 12.998(2) ?, b = 27.058(3) ?, c = 17.962(2) ?, beta = 99.74(1) degrees, V = 6225(1) ?(3), Z = 2; 2,DME/hexanes, P2(1)/n, a = 23.335(2) ?, b = 12.649(1) ?, c = 27.175(3) ?, beta = 96.36(1) degrees, V = 7971(1) ?(3), Z = 4, 2788 reflections (I > 3sigma(I)), R(F)() = 9.5%; 3, THF, P2(1), a = 12.898(1) ?, b = 16.945(1) ?, c = 13.290(1) ?, beta = 118.64(2) degrees, V = 2549.3(3) ?(3), Z = 2, 3414 reflections (I > 3sigma(I)), R(F)() = 4.3%; 4a, hexanes, P2(1), a = 9.718(2) ?, b = 19.119(3) ?, c = 12.640(2) ?, beta = 112.08(1) degrees, V = 2176.3(6) ?(3), Z = 2, 2933 reflections (I > 3sigma(I)), R(F)() = 4.3%; 4b, hexanes, 158 K, a = 9.729(2) ?, b = 19.095(5) ?, c = 12.744(1) ?, beta = 112.11(1) degrees, V = 2193.4(6) ?(3); 5b, hot toluene, 158 K, P2(1), a =19.218(9) ?, b = 9.375(3) ?, c = 19.820(5) ?, beta = 110.25(2) degrees, V = 3350(2)?(3), Z = 2, 1718 reflections (I > 2sigma (I)), R1 = 9.7%; 7, hexanes, 156 K, P&onemacr;, a = 9.618(3) ?, b = 12.738(4) ?, c = 9.608(3) ?, alpha = 99.32(1) degrees, beta = 108.87(1) degrees, gamma = 94.23(1) degrees, V = 1089.1(6) ?(3), Z = 2, 2976 reflections (I > 3sigma(I)), R(F)() = 3.9%; 8, hexanes, 156 K, Pcab, a = 23.510(5) ?, b = 25.462(5) ?, c = 8.668(2) ?, V = 5188(1) ?(3), Z = 8, 1386 reflections (I > 3sigma(I)), R(F)() = 5.7%.     

Terphenyl substituted derivatives of manganese(II): distorted geometries and resistance to elimination

Reaction of {Li(THF)Ar'MnI(2)}(2) (Ar' = C(6)H(3)-2,6-(C(6)H(2)-2,6-(i)Pr(3))(2)) with LiAr', LiC≡CR (R = (t)Bu or Ph), or (C(6)H(2)-2,4,6-(i)Pr(3))MgBr(THF)(2) afforded the diaryl MnAr'(2) (1), the alkynyl salts Ar'Mn(C≡C(t)Bu)(4){Li(THF)}(3) (2) and Ar'Mn(C≡CPh)(3)Li(3)(THF)(Et(2)O)(2)(μ(3)-I) (3), and the manganate salt {Li(THF)}Ar'Mn(μ-I)(C(6)H(2)-2,4,6-(i)Pr(3)) (4), respectively. Complex 4 reacted with one equivalent of (C(6)H(2)-2,4,6-(i)Pr(3))MgBr(THF)(2) to afford the homoleptic dimer {Mn(C(6)H(2)-2,4,6-(i)Pr(3))(μ-C(6)H(2)-2,4,6-(i)Pr(3))}(2) (5), which resulted from the displacement of the bulkier Ar' ligand in preference to the halogen. The reaction of the more crowded {Li(THF)Ar*MnI(2)}(2) (Ar* = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-(i)Pr(3))(2)) with Li(t)Bu gave complex Ar*Mn(t)Bu (6). Complex 1 is a rare monomeric homoleptic two-coordinate diaryl Mn(II) complex; while 6 displays no tendency to eliminate β-hydrogens from the (t)Bu group because of the stabilization supplied by Ar*. Compounds 2 and 3 have cubane frameworks, which are constructed from a manganese, three carbons from three acetylide ligands, three lithiums, each coordinated by a donor, plus either a carbon from a further acetylide ligand (2) or an iodide (3). The Mn(II) atom in 4 has an unusual distorted T-shaped geometry while the dimeric 5 features trigonal planar manganese coordination. The chloride substituted complex Li(2)(THF)(3){Ar'MnCl(2)}(2) (7), which has a structure very similar to that of {Li(THF)Ar'MnI(2)}(2), was also prepared for use as a possible starting material. However, its generally lower solubility rendered it less useful than the iodo salt. Complexes 1-7 were characterized by X-ray crystallography and UV-vis spectroscopy. Magnetic studies of 2-4 and 6 showed that they have 3d(5) high-spin configurations.     

Binuclear half-metallocene chromium(III) complexes mediated ethylene polymerization with alkylaluminium as cocatalyst

Binuclear half-metallocene chromium complexes {Cp*[3-(CH==NR)-2-O-C(10)H(5)]CrCl}(2) [Cp* = C(5)Me(5); R = (i)Pr (1), Ph (2), 2,6-(i)Pr(2)C(6)H(3) (3)] based on 1,1'-binaphthyl ligands, as well as their mononuclear analogues Cp*[3-(CH==NR)-2'-R'-2-O-C(20)H(11)]CrCl [R = (i)Pr, R' = (n)BuO (4), R = Ph, R' = (n)BuO (5), R = 2,6-(i)Pr(2)C(6)H(3), R' = (n)BuO (6), R = (i)Pr, R' = H (7)], were synthesized and characterized by mass spectrometry, elemental analysis, magnetic measurement, and UV-vis spectroscopy. The molecular structures of complexes 1, 3, 5 and 6 were further confirmed by single-crystal X-ray crystallographic analysis. When activated with a small amount of AlMe(3), these binuclear complexes exhibited higher activities in catalyzing ethylene polymerization in comparison with their mononuclear analogues, affording high molecular weight polymers with unimodal molecular weight distributions. The highest activity up to 2.87 × 10(6) g PE (mol Cr)(-1) h(-1) was achieved in the catalyst system of complex 3 bearing a bulky 2,6-(i)Pr(2)C(6)H(3) group on the imine nitrogen atom in the presence of 25 equiv. AlMe(3) as activator at 20 °C. (13)C NMR analysis indicates the resultant polymers are linear and no evidence on branch was found.     

Rare earth metal bis(amide) complexes bearing amidinate ancillary ligands: synthesis, characterization, and performance as catalyst precursors for cis-1,4 selective polymerization of isoprene

A family of rare earth metal bis(amide) complexes bearing monoanionic amidinate [RC(N-2,6-Me(2)C(6)H(3))(2)](-) (R = cyclohexyl (Cy), phenyl (Ph)) as ancillary ligands were synthesized and characterized. One-pot salt metathesis reaction of anhydrous LnCl(3) with one equivalent of amidinate lithium [RC(N-2,6-Me(2)C(6)H(3))(2)]Li, following the introduction of two equivalents of NaN(SiMe(3))(2) in THF at room temperature afforded the neutral and unsolvated mono(amidinate) rare earth metal bis(amide) complexes [RC(N-2,6-Me(2)C(6)H(3))(2)]Y[N(SiMe(3))(2)](2) (R = Cy (1); R = Ph (2)), and the "ate" mono(amidinate) rare earth metal bis(amide) complex [CyC(N-2,6-Me(2)C(6)H(3))(2)]Lu[N(SiMe(3))(2)](2)(μ-Cl)Li(THF)(3) (3) in 61-72% isolated yields. These complexes were characterized by elemental analysis, NMR spectroscopy, FT-IR spectroscopy, and X-ray single crystal diffraction. Single crystal structural determination revealed that the central metal in complexes 1 and 2 adopts a distorted tetrahedral geometry, and in complex 3 forms a distorted trigonal bipyramidal geometry. In the presence of AlMe(3), and in combination with one equimolar amount of [Ph(3)C][B(C(6)F(5))(4)], complexes 1 and 2 showed high activity towards isoprene polymerization to give high molecular weight polyisoprene (M(n) > 10(4)) with good cis-1,4 selectivity (>90%).     

Synthesis, characterization, and reactivity of rhodium(I) acetylacetonato complexes containing pyridinecarboxaldimine ligands

Addition of o-C 6H 4NCHNAr to Rh(coe) 2(acac) (coe = cis-cyclooctene, acac = acetylacetonato) gave several new iminopyridine rhodium(I) complexes of the type Rh(acac)(kappa (2)- o-C 6H 4 NCH NAr) ( 1a Ar = 4-C 6H 4-OMe; 1b Ar = 2,6-C 6H 3-Me 2; 1c Ar = 2,6-C 6H 3-Et 2; 1d Ar = 2,6-C 6H 3- i-Pr 2). All new rhodium complexes have been characterized by a number of physical methods, including multinuclear NMR spectroscopy and X-ray diffraction studies for 1b and 1c. Addition of CHCl 3 to 1a afforded the corresponding rhodium(III) complex trans-Rh(kappa (2)- o-C 6H 4 NCH NAr)(CHCl 2)(Cl)(acac) ( 2). Addition of B 2cat 3 (cat = 1,2-O 2C 6H 4) to 1 gave zwitterionic Rh(eta (6)-catBcat)(kappa (2)- o-C 6H 4 NCH NAr) ( 3). The molecular structure of 3b has been confirmed by a single crystal X-ray diffraction study and shows that the N 2Rh fragment is bound to the catBcat anion via one of the catecholato groups in a eta (6)-fashion. These complexes have also been examined for their ability to catalyze the hydroboration of a series of vinylarenes. Reactions using catecholborane and pinacolborane seem to proceed largely through a dehydrogenative borylation mechanism to give a number of boronated products.     

Synthesis of vanadium(III) complexes bearing iminopyrrolyl ligands and their role as thermal robust ethylene (co)polymerization catalysts

Bis(imino)pyrrolyl vanadium(III) complexes 2a-e [2,5-C(4)H(2)N(CH=NR)(2)]VCl(2)(THF)(2) [R = C(6)H(5) (2a), 2,6-Me(2)C(6)H(3) (2b), 2,6-(i)Pr(2)C(6)H(3) (2c), 2,4,6-Me(3)C(6)H(2) (2d), C(6)F(5) (2e)] and bis(iminopyrrolyl) vanadium(III) complex 4f [C(4)H(3)N(CH=N-2,6-(i)PrC(6)H(3))](2)VCl(THF) have been prepared in good yields from VCl(3)(THF)(3) by treating with 1.0 and 2.0 equivalent deprotonated ligands in tetrahydrofuran (THF), respectively. These complexes were characterized by FTIR and mass spectra as well as elemental analysis. Structures of 2c and 4f were further confirmed by X-ray crystallographic analysis. DFT calculations indicated the configurations of 2a-e with two nitrogen atoms of the chelating ligand coordinating with vanadium metal centre were more stable in energy. These complexes were employed as catalysts for ethylene polymerization at various reaction conditions. On activation with Et(2)AlCl, these complexes exhibited high catalytic activities (up to 22.2 kg mmol(-1)(V) h(-1) bar(-1)) even at high temperature, suggesting these catalysts possessed remarkable thermal stability. Moreover, high molecular weight polymer with unimodal molecular weight distributions can be obtained, indicating the polymerization took place in a single-site nature. The copolymerizations of ethylene and 1-hexene with precatalysts 2a-e and 4f were also explored in the presence of Et(2)AlCl. Catalytic activity, comonomer incorporation, and properties of the resultant polymers can be controlled over a wide range by tuning catalyst structures and reaction parameters.     

Highly trans-1,4 selective (co-)polymerization of butadiene and isoprene with quinolyl anilido rare earth metal bis(alkyl) precursors

The N-R-quinolinyl-8-amino ligands HL(1-3) (R = 2,6-(i)Pr(2)C(6)H(3) (HL(1)), 2,6-Et(2)C(6)H(3) (HL(2)), 2,6-Me(2)C(6)H(3) (HL(3))) have been prepared, which reacted readily with one equiv. of rare earth metal tris(alkyl)s to afford the corresponding bis(alkyl) complexes L(1)Y(CH(2)SiMe(3))(2)(THF) (1) and L(1-3)Lu(CH(2)SiMe(3))(2)(THF) (2-4) via alkane elimination. Contrastingly, treatment of the in situ generated neodymium tri(alkyl)s with HL(1) afforded a mono(alkyl) neodymium complex (5). Complexes 1, 2 and 5 in combination with aluminium alkyls and organoborates established homogenous ternary systems that exhibited versatile catalytic activities and trans-1,4 selectivities for the polymerization of butadiene, depending on the types of aluminium alkyl, organoborate and rare earth metal used. Furthermore, the trans-1,4 selective copolymerization of butadiene and isoprene was achieved by using the ternary system of 1/AlMe(3)/[Ph(3)C][B(C(6)F(5))(4)]. Both the kinetics of copolymerization and the thermal behavior of the copolymers were investigated.     

Ligand-controlled synthesis of vanadium(I) β-diketiminates and their catalysis in cyclotrimerization of alkynes

Three dimeric vanadium(I) β-diketiminates [V{μ-(η(6)-ArN)C(Me)CHC(Me)C(N-Ar)}](2) (Ar = 2,6-Me(2)C(6)H(3) (2), 2,6-Et(2)C(6)H(3) (3), 9-anthracenyl (4)) were prepared and isolated upon reduction of their corresponding dichloro precursors VCl(2)(Nacnac). Compounds 2-4 all show a structure with each vanadium atom being η(2) bonded to the β-diketiminate framework and η(6) bonded to a flanking ring of a β-diketiminato ligand, attached to the other vanadium centre within the dimer. No metal-metal bonding interactions are observed in these dimers due to long vanadium-vanadium separations. Compounds 2-4 display an antiferromagnetic exchange between the two vanadium centres. An imido azabutadienyl complex (η(2)-PhCC(H)C(Ph)NC(6)H(3)-2,6-(i)Pr(2))VN(C(6)H(3)-2,6-(i)Pr(2))(OEt(2)) (5) was isolated from the reduction of VCl(2)(HC(C(Ph)NC(6)H(3)-2,6-(i)Pr(2))(2)) by KC(8). Compounds 2-4 and the inverted-sandwich divanadium complex (μ-η(6):η(6)-C(6)H(5)Me)[V(HC(C(Me)NC(6)H(3)-2,6-(i)Pr(2))(2))](2) (1) reduce Ph(2)S(2) to give two vanadium dithiolates V(SPh)(2)[(HC(C(Me)NC(6)H(3)-2,6-R(2))(2))] (R = Et (6), (i)Pr (7)) through an oxidative addition. Most notably, 1 and 3 catalyze the cyclotrimerization of alkynes, giving tri-substituted benzenes in good yields and a 1,3,5-triphenylbenzene coordinated intermediate 8 was isolated and characterized.     

Synthesis, characterization, and electronic structure of diimine complexes of chromium

We have prepared and structurally characterized several complexes of chromium coordinated by diimine (or 1,4-diazadiene) ligands, that is, Ar-N=C(R)-(R)C=N-Ar (RL(Ar)) (where Ar = 2,6-diisopropylphenyl ("iPr") or 2,6-dimethylphenyl ("Me") and R = H or Me). The reaction of CrCl2 with HLiPr gave dinuclear [(HLiPr)Cr]2(mu-Cl)3(Cl)(THF) when isolated from Et2O; in THF solution, however, the product exists as mononuclear (HLiPr)CrCl2(THF)2. Two isostructural derivatives, (MeLMe)CrCl2(THF)2 and (HL(Me))CrCl2(THF)2, have also been prepared. Furthermore, the bis-ligand complex, (HLiPr)2Cr, has been prepared along with its reduction product, Li(THF)4[(HLiPr)2Cr]. We have also synthesized the tetracarbonyl complex, (HLiPr)Cr(CO)4, by addition of HLiPr to Cr(CO)4(NCCH3)2. The structure and variable temperature magnetic susceptibility of the previously reported Cr halide dimer, [(HLiPr)Cr(mu-Cl)]2, is also discussed in detail. All of the diimine complexes have been characterized structurally, spectroscopically, and magnetically, and their electronic structures are discussed with the aid of density-functional theory calculations.     

Synthesis and characterization of three-coordinate and related beta-diketiminate derivatives of manganese,iron, and cobalt

Treatment of M[N(SiMe(3))(2)](2) (M = Mn, Fe, Co) with various bulky beta-diketimines afforded a variety of new three-coordinate complexes which were characterized by UV-vis, (1)H NMR and IR spectroscopy, magnetic measurements, and X-ray crystallography. Reaction of the beta-diketimine H(Dipp)NC(Me)CHC(Me)N(Dipp) (Dipp(2)N(wedge)NH; Dipp = C(6)H(3)-2,6-Pr(i)(2)) with M[N(SiMe(3))(2)](2) (M = Mn or Co) gave Dipp(2)N(wedge)NMN(SiMe(3))(2) (M = Mn, 1; Co, 3) while the reaction of Fe[N(SiMe(3))(2)](2) with Ar(2)N(wedge)NH (Ar = Dipp, C(6)F(5), Mes, C(6)H(3)-2,6-Me(2), or C(6)H(3)-2,6-Cl(2)) afforded the series of iron complexes Ar(2)N(wedge)NFe[N(SiMe(3))(2)] (Ar = Dipp, 2a; C(6)F(5), 2b; Mes, 2c; C(6)H(3)-2,6-Me(2), 2d; C(6)H(3)-2,6-Cl(2), 2e). This represents a new synthetic route to beta-diketiminate complexes of these metals. The four-coordinate bis-beta-diketiminate complex Fe[N(wedge)N(C(6)F(5))(2)](2), 4, was also isolated as a byproduct from the synthesis of 2b. Direct reaction of the Dipp(2)N(wedge)NLi with CoCl(2) gave the "ate" salt Dipp(2)N(wedge)NCoCl(2)Li(THF)(2), 5, in which the lithium chloride has formed a complex with Dipp(2)N(wedge)NCoCl through chloride bridging. The Fe(III) species Dipp(2)N(wedge)NFeCl(2), 6, was obtained cleanly from the reaction of FeCl(3) with Dipp(2)N(wedge)NLi. Magnetic measurements showed that all the complexes have a high spin configuration. The different substituents in the series of iron complexes 2a-e allowed assignment of their paramagnetically shifted (1)H NMR spectra. The X-ray crystal structures 1-2d and 3 showed that they have a distorted three-coordinate planar configuration at the metals whereas complexes 4-6 have highly distorted four-coordinate geometries.     

Reduction of sterically hindered β-diketiminato europium(III) complexes by the β-diketiminato anion: a convenient route for the synthesis of β-diketiminato europium(II) complexes

The metathesis reaction of anhydrous EuCl(3) with sodium salt of bulky β-diketiminato NaL (L = [N(2, 4, 6- Me(3)C(6)H(2))C(Me)](2)CH(-), L(2, 4, 6-Me3); [N(2,6-(i)Pr(2)C(6)H(3))C(Me)](2)CH(-), L(2, 6-ipr2) and [(2, 6-(i)Pr(2)C(6)H(3))NC(Me)CHC(Me)N(C(6)H(5))](-), L(2, 6-ipr2)(Ph)) in THF at 60 °C afforded the corresponding Eu(II) complexes: Eu(II)(L(2, 4, 6-Me3))(2)(THF) (1), Eu(II)(L(2, 6-ipr2))(2) (2) and Eu(II)(L(2, 6-ipr2)(Ph))(2) (5) with the formations of dimers (L(2, 4, 6-Me3))(2) (3) and (L(2, 6-ipr2))(2) (4) for the former two reactions and proligand L(2, 6-ipr2)(Ph)H (6) for the latter one. Compounds 1-6 were confirmed by an X-ray crystal structure analysis. The central metal Eu(II) in 1 is coordinated by two monoanionic L(2, 4, 6-Me3) ligands and one THF molecule in a trigonal bipyramid. The Eu(II) in each of 2 and 5 is ligated by two monoanionic ligands to form a tetrahedral geometry. The BVS (Bond Valence Sum) calculation indicates the oxidation state of Eu in all the three complexes is 2+ (2.12 for 1, 1.86 for 2 and 1.99 for 5). The isolation of dimers of (L(2, 4, 6-Me3))(2) and L(2, 6-ipr2))(2) and proligand L(2, 6-ipr2)(Ph)H demonstrates that the reducing agent in the present reduction of a Eu(III) ion to a Eu(II) ion might be the (L(2, 4, 6-Me3))(-), (L(2, 6-ipr2))(-) and (L(2, 6-ipr2)(Ph))(-), respectively. The possible mechanism for the reduction pathway is presented.     

Monoalkyl and monoanilide yttrium complexes containing tridentate pyridyl-1-azaallyl dianionic ligands

A series of pyridyl-1-azaallyl ligand precursors (HL1-HL5) were synthesized via condensation of pyridine ketones with anilines. The alkane elimination reactions between Y(CH(2)SiMe(3))(3)(THF)(2) and HL4 or HL5 gave the monoalkyl complexes (L4-H)YCH(2)SiMe(3)(THF) (1) and (L5-H)YCH(2)SiMe(3)(THF) (2) supported by new tridentate pyridyl-1-azaallyl dianionic ligands. The reactions of monoalkyl complexes, 1 and 2, with one equivalent of 2,6-diisopropylaniline produced the corresponding monoanilide complexes, (L4-H)YNHAr(THF) (3) and (L5-H)YNHAr(THF) (4) (Ar = 2,6-((i)Pr)(2)C(6)H(3)), via highly selective protonolysis of the terminal alkyl Y-CH(2)SiMe(3) bond. Complexes 1-4 are active for intramolecular hydroamination of aminoalkenes.     

Cyclopentadienyl chromium diimine and pyridine-imine complexes: ligand-based radicals and metal-based redox chemistry

Paramagnetic CpCr(III) complexes with antiferromagnetically-coupled anionic radical diimine and pyridine-imine ligands were prepared and characterized. The diimine chloro CpCr[(ArNCR)(2)]Cl complexes (1: Ar = 2,6-iPr(2)C(6)H(3) (Dpp), R = H; 2: Ar = 2,6-Me(2)C(6)H(3) (Xyl), R = Me; 3: Ar = 2,4,6-Me(3)C(6)H(2) (Mes), R = Me) were synthesized by treatment of previously reported Cr(diimine)(THF)(2)Cl(2) precursors with NaCp. Reduction of 1 with Zn gives CpCr[(DppNCH)(2)], 4, resulting from reduction of Cr(III) to Cr(II) with retention of the ligand-based radical. Alkoxide complexes CpCr[(DppNCH)(2)](OCR(2)R') (5: R = Me, R' = Ph; 6: R = iPr, R' = H) were synthesized by protonolysis of Cp(2)Cr with HOCR(2)R' in the presence of the neutral diimine and catalytic base. The corresponding radical pyridine-imine complexes CpCr(PyCHNMes)Cl (9), CpCr(PyCHNMes) (8), and CpCr(PyCHNMes)(OCMe(2)Ph) (11), were prepared by analogous routes. Oxidation of 8 with iodine gives CpCr(PyCHNMes)I (10) where oxidation of Cr(II) to Cr(III) again occurs with retention of the anionic pyridine-imine radical ligand. The molecular structures of complexes 1, 2, 4-8, 10 and 11 were determined by single-crystal X-ray diffraction. Unusual low energy bands were observed in the UV-vis spectra of the reported complexes, with particularly strong transitions observed for the Cr(II) complexes 4 and 8. The electronic structure of pyridine-imine complexes 8 and 10 were investigated by theoretical calculations.     

Synthesis and reactivity of cationic niobium and tantalum methyl complexes supported by imido and β-diketiminato ligands

The synthesis and reactivity of the cationic niobium and tantalum monomethyl complexes [(BDI)MeM(N(t)Bu)][X] (BDI = [Ar]NC(CH(3))CHC(CH(3))N[Ar], Ar = 2,6-(i)Pr(2)C(6)H(3); M = Nb, Ta; X = MeB(C(6)F(5))(3), B(C(6)F(5))(4)] was investigated. The cationic alkyl complexes failed to irreversibly bind CO but formed phosphine-trapped acyl complexes [(BDI)(R(3)PC(O)Me)M(N(t)Bu)][B(C(6)F(5))(4)] (R = Et, Cy) in the presence of a combination of trialkylphosphines and CO. Treatment of the monoalkyl cationic Nb complex with XylNC (Xyl = 2,6-Me(2)-C(6)H(3)) resulted in irreversible formation of the iminoacyl complex [(BDI)(XylN[double bond, length as m-dash]C(Me))Nb(N(t)Bu)][B(C(6)F(5))(4)], which did not bind phosphines but would add a methide group to the iminoacyl carbon to provide the known ketimine complex (BDI)(XylNCMe(2))Nb(N(t)Bu). Further stoichiometric chemistry explored i) migratory insertion reactions to form new alkoxide, amidinate, and ketimide complexes; ii) protonolysis reactions with Ph(3)SiOH to form thermally robust cationic siloxide complexes; and iii) catalytic high-density polyethylene formation mediated by the cationic Nb methyl complex.