Amide-silyl ligand exchanges and equilibria among group 4 amide and silyl complexes

M(NMe2)4 (M = Zr, 1a; Hf, 1b) and the silyl anion (SiButPh2)- (2) in Li(THF)2SiButPh2 (2-Li) were found to undergo a ligand exchange to give [M(NMe2)3(SiButPh2)2]- (M = Zr, 3a; Hf, 3b) and [M(NMe2)5]- (M = Zr, 4a; Hf, 4b) in THF. The reaction is reversible, leading to equilibria: 2 1a (or 1b) + 2 2 <--> 3a (or 3b) + 4a (or 4b). In toluene, the reaction of 1a with 2 yields [(Me2N)3Zr(SiButPh2)2]-[Zr(NMe2)5Li2(THF)4]+ (5) as an ionic pair. The silyl anion 2 selectively attacks the -N(SiMe3)2 ligand in (Me2N)3Zr-N(SiMe3)2 (6a) to give 3a and [N(SiMe3)2]- (7) in reversible reaction: 6a + 2 2 <--> 3a + 7. The following equilibria have also been observed and studied: 2M(NMe2)4 (1a; 1b) + [Si(SiMe3)3]- (8) <--> (Me2N)3M-Si(SiMe3)3 (M = Zr, 9a; Hf, 9b) + [M(NMe2)5]- (M = Zr, 4a; Hf, 4b); 6a (or 6b) + 8 <--> 9a (or 9b) + [N(SiMe3)2]- (7). The current study represents rare, direct observations of reversible amide-silyl exchanges and their equilibria. Crystal structures of 5, (Me2N)3Hf-Si(SiMe3)3 (9b), and [Hf(NMe2)4]2 (dimer of 1b), as well as the preparation of (Me2N)3M-N(SiMe3)2 (6a; 6b) are also reported.     

Hf3 cluster is triply (sigma-, pi-, and delta-) aromatic in the lowest D3h, 1A1' state

The extensive search for the global minimum structure of Hf3 at the B3LYP/LANL2DZ level of theory revealed that D3h 3A2' (1a1'(2)1a2'(2)1e'(4)2a1'(2)1e'2) and D3h 1A1' (1a1'(2)2a1'(2)1e'(4)1a2'(2)3a1'2) are the lowest triplet and singlet states, respectively, with the triplet state being the lowest one. However, at the CASSCF(10,14)/Stuttgart+2f1g level of theory these two states are degenerate, indicating that at the higher level of theory the singlet state could be in fact the global minimum structure. The triplet D3h 3A2' (1a1'21a2'(2)1e'(4)2a1'(2)1e'2) structure is doubly (sigma- and pi-) aromatic and the singlet D3h 1A1' (1a1'(2)2a1'(2)1e'(4)1a2'(2)3a1'2) structure is the first reported triply (sigma-, pi-, and delta-) aromatic system.     

Insertion of CO2, CS2, and COS into iron(II)-hydride bonds

The reactions between cis-Fe(dmpe)2H2 (dmpe = Me2PCH2CH2PMe2) (1) or cis-Fe(PP3)H2 (PP3 = P(CH2CH2PMe2)3) (2) and carbon dioxide (CO2), carbon disulfide (CS2), and carbonyl sulfide (COS) are investigated. At 300 K, additions of CO2 (1 atm), CS2 (2 equiv), and COS (1 atm) to 1 result in the formation of a stable transformato hydride, trans-Fe(dmpe)2(OCHO)H (3a), a trans-dithioformato hydride, trans-Fe(dmpe)2(SCHS)H (4a), and a trans-thioformato hydride, trans-Fe(dmpe)2(SCHO)H (5a), respectively. When CS2 and COS are added to cis-Fe(dmpe)2H2 at 195 K, a cis-dithioformato hydride, 4b, and a cis-thioformato hydride, 5b, respectively, are observed as the initially formed products, but there is no evidence of the corresponding cis-formato hydride upon addition of CO2 to cis-Fe(dmpe)2H2. Additions of excess CO2, CS2, and COS to 1 at lower temperatures (195-240 K) result in the formation of a trans-bis(formate), trans-Fe(dmpe)2(OCHO)2 (3b), a trans-bis(dithioformate), trans-Fe(dmpe)2(SCHS)2 (4c), and a cis-bis(thioformate), cis-Fe(dmpe)2(SCHO)2 (5c), respectively. trans-Fe(dmpe)2(SCHO)2 (5d) is prepared by the addition of excess COS at 300 K. Additions of CO2 (1 atm), CS2 (0.75 equiv), and COS (1 atm) to 2 at 300 K result in the formation of a thermally stable, geometrically constrained cis-formato hydride, cis-Fe(PP3)(OCHO)H (6a), a cis-dithioformato hydride, cis-Fe(PP3)(SCHS)H (7a), and a cis-thioformato hydride, cis-Fe(PP3)(SCHO)H (8a), respectively. Additions of excess CO2 and COS to 2 yield a cis-bis(formate), cis-Fe(PP3)(OCHO)2 (6b), and a thermally stable cis-bis(thioformate), cis-Fe(PP3)(SCHO)2 (8b), respectively. All complexes are characterized by multinuclear NMR spectroscopy, with IR spectroscopy and elemental analyses confirming structures of thermally stable complexes where possible. Complexes 3b and 5a are also characterized by X-ray crystallography.     

Ni(II), Pd(II) and Pt(II) complexes of PNP and PSP tridentate amino-phosphine ligands

The ligands D((CH(2))(2)NHPiPr(2))(2) (D = NH 1, S 2) react with (dme)NiCl(2) or (PhCN)(2)MCl(2) (M = Pd, Pt) to give complexes of the form [D((CH(2))(2)NHPiPr(2))(2)MX]X (X = Cl, I; M = Ni, Pd, Pt) which were converted to corresponding iodide derivatives by reaction with Me(3)SiI. Reaction of 1 or 2 with (COD)PdMeCl affords facile routes to [κ(3)P,N,P-NH((CH(2))(2)NHPiPr(2))(2)PdMe]Cl (8a) and [κ(3)P,S,P-S((CH(2))(2)NHPiPr(2))(2)PdMe]Cl (9a) in high yields. An alternative synthetic approach involves oxidative addition of MeI to a M(0) precursor yielding [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)NiMe]I (10), [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)MMe]I (M = Pd 8b Pt 11) and [κ(3)P,S,P-S(CH(2)CH(2)NHPiPr(2))(2)MMe]I (M = Pd 9b, Pt 12). Alternatively, use of NEt(3)HCl in place of MeI produces the species [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)MH]X (X = Cl, M = Ni 13a, Pd 14a, Pt 16a). The analogs containing 2; [κ(3)P,S,P-S((CH(2))(2)NHPiPr(2))(2)MH]X (M = Pd, X = PF(6)15: M = Pt, X = Br, 17a, PF(6)17b) were also prepared in yields ranging from 74-93%. In addition, aryl halide oxidative addition was also employed to prepare [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)MC(6)H(4)F]Cl (M = Ni 18, Pd 19) and [κ(3)P,S,P-S((CH(2))(2)NHPiPr(2))(2)Pd(C(6)H(4)F)]Cl (20). Crystal structures of 3a, 4a, 5a, 6a, 8a, 9a, 14b and 16b are reported.     

Controlled assembly of ruthenium complexes through ortho-carborane dithiolate and polysulfide ligands

Treatment of ortho-carborane, n-butyl lithium, sulfur, and [(p-cymene)RuCl(2)](2) in varying ratio led to four new compounds (p-cymene)Ru[S(3)(C(2)B(10)H(10))(2)] (3), [(p-cymene)Ru(2)(μ(2)-S(2)C(2)B(10)H(9))(μ(3)-S(2)C(2)B(10)H(10))](2) (4), [(p-cymene)Ru](2)Ru(μ(2)-η(2):η(2)-S(2)) (μ(2)-η(2):η(1)-S(2)Cl)(μ(2)-S(2)C(2)B(10)H(10))(2) (5), and [(p-cymene)Ru](2)Ru(μ(2)-η(1):η(1)-S(2))(μ(3)-η(2):η(2)-S(4)) (μ(2)-S(2)C(2)B(10)H(10))(2) (6), respectively. In 3, the ruthenium atom is coordinated by three S atoms from a in situ generated tridentate [S(3)(C(2)B(10)H(10))(2)](2-) ligand. 4 consists of two identical dinuclear (p-cymene)Ru(2)(μ(2)-S(2)C(2)B(10)H(9))(μ(3)-S(2)C(2)B(10)H(10)) subunits which connect to each other via the Ru-Ru bond and two bridging o-carborane-1,2-dithiolate ligands. In 4, a Ru-B bond is present. 5 contains a Ru(3)(μ(2)-S)(2)(μ(2)-S(2))(μ(2)-S(2)Cl) core, and the central ruthenium atom is coordinated by seven S atoms in a distorted pentagonal bipyramidal geometry. In 5, a S-Cl bond is generated. 6 has a novel Ru(3)(μ(2)-S)(2)(μ(2)-S(2))(μ(3)-S(4)) core, and the three ruthenium atoms are connected through the two terminal sulfur atoms of the S-S-S-S chain in a μ(3) binding fashion. All the four complexes have been characterized by elemental analysis, mass, NMR, and X-ray crystallography.     

Formation of organolithium hetero-aggregates [Li4Ar2(nBu)2] (Ar=C6H4CH(Me)NMe2-2) during the directed ortho-lithiation of [1-(dimethylamino)ethyl]benzene

(R)-[1-(Dimethylamino)ethyl]benzene reacts with nBuLi in a 1:1 molar ratio in pentane to quantitatively yield a unique hetero-aggregate (2 a) containing the lithiated arene, unreacted nBuLi, and the complexed parent arene in a 1:1:1 ratio. As a model compound, [Li(4)(C(6)H(4)CH(Me)NMe(2)-2)(2)(nBu)(2)] (2 b) was prepared from the quantitative redistribution reaction of the parent lithiated arene Li(C(6)H(4)CH(Me)NMe(2)-2) with nBuLi in a 1:1 molar ratio. The mono-Et(2)O adduct [Li(4)(C(6)H(4)CH(Me)NMe(2)-2)(2)(nBu)(2)(OEt(2))] (2 c) and the bis-Et(2)O adduct [Li(4)(C(6)H(4)CH(Me)NMe(2)-2)(2)(nBu)(2)(OEt(2))(2)] (2 d) were obtained by re-crystallization of 2 b from pentane/Et(2)O and pure Et(2)O, respectively. The single-crystal X-ray structure determinations of 2 b-d show that the overall structural motifs of all three derivatives are closely related. They are all tetranuclear Li aggregates in which the four Li atoms are arranged in an almost regular tetrahedron. These structures can be described as consisting of two linked dimeric units: one Li(2)Ar(2) dimer and a hypothetical Li(2)nBu(2) dimer. The stereochemical aspects of the chiral Li(2)Ar(2) fragment are discussed. The structures as observed in the solid state are apparently retained in solution as revealed by a combination of cryoscopy and (1)H, (13)C, and (6)Li NMR spectroscopy.     

Anionic Roussin's red esters (RREs) syn-/anti-[Fe(mu-SEt)(NO)2]2(-): the critical role of thiolate ligands in regulating the transformation of RREs into dinitrosyl iron complexes and the anionic RREs

The anionic syn-/ anti-[Fe(mu-SEt)(NO) 2] 2 (-) ( 2a) were synthesized and characterized by IR, UV-vis, EPR, and X-ray diffraction. The geometry of the [Fe(mu-S) 2Fe] core is rearranged in going from [{Fe(NO) 2} (9)-{Fe(NO) 2} (9)] Roussin's red ester [Fe(mu-SEt)(NO) 2] 2 ( 1a) (Fe...Fe distance of 2.7080(5) A) to the [{Fe(NO) 2} (9)-{Fe(NO) 2} (10)] complex 2a (Fe...Fe distance of 2.8413(6) A) to minimize the degree of Fe...Fe interaction to stabilize complex 2a. On the basis of X-ray absorption (Fe K- and L-edge), EPR and SQUID, complex 2a is best described as the anionic [{Fe(NO) 2} (9)-{Fe(NO) 2} (10)] Roussin's red ester with the fully delocalized mixed-valence core. The complete bridged-thiolate cleavage yielded DNIC [(EtS) 2Fe(NO) 2] (-) ( 3a) in the reaction of 2 equiv of [EtS] (-) and complex 1a, whereas reaction of 2 equiv of [(t)BuS] (-) with [Fe(micro-S (t)Bu)(NO) 2] 2 (1b) gave DNIC [((t)BuS) 2Fe(NO) 2] (-) (3b) and the anionic Roussin's red ester [Fe(mu-S (t)Bu)(NO) 2] 2 (-) (2b) through bridged-thiolate cleavage in combination with reduction. In contrast to the inertness of DNIC 3b toward complex 1b, nucleophile DNIC 3a induces the reduction of complex 1a to produce the anionic Roussin's red ester 2a. Interestingly, dissolution of complex 3a in MeOH at 298 K finally led to the formation of a mixture of complexes 2a and 3a, in contrast to the dynamic equilibrium of complexes 3b and 1b observed in dissolution of complex 3b in MeOH. These results illustrate the aspect of how the steric structures of nucleophiles ([EtS] (-) vs [ (t)BuS] (-) and [(EtS) 2Fe(NO)2](-) vs [((t)BuS) 2Fe(NO)2] (-)) function to determine the reaction products.     

Synthesis and Characterization of Sterically Encumbered Derivatives of Aluminum Hydrides and Halides: Assessment of Steric Properties of Bulky Terphenyl Ligands

The synthesis and characterization of several sterically encumbered monoterphenyl derivatives of aluminum halides and aluminum hydrides are described. These compounds are [2,6-Mes(2)C(6)H(3)AlH(3)LiOEt(2)](n)() (1), (Mes = 2,4,6-Me(3)C(6)H(2)-), 2,6-Mes(2)C(6)H(3)AlH(2)OEt(2) (2), [2,6-Mes(2)C(6)H(3)AlH(2)](2) (3), 2,6-Mes(2)C(6)H(3)AlCl(2)OEt(2) (4), [2,6-Mes(2)C(6)H(3)AlCl(3)LiOEt(2)](n)() (5), [2,6-Mes(2)C(6)H(3)AlCl(2)](2) (6), TriphAlBr(2)OEt(2) (7), (Triph = 2,4,6-Ph(3)C(6)H(2)-), [2,6-Trip(2)C(6)H(3)AlH(3)LiOEt(2)](2) (8) (Trip = 2,4,6-i-Pr(3)C(6)H(2)-), 2,6-Trip(2)C(6)H(3)AlH(2)OEt(2) (9), [2,6-Trip(2)C(6)H(3)AlH(2)](2) (10), 2,6-Trip(2)C(6)H(3)AlCl(2)OEt(2) (11), and the partially hydrolyzed derivative [2,6-Trip(2)C(6)H(3)Al(Cl)(0.68)(H)(0.32)(&mgr;-OH)](2).2C(6)H(6) (12). The structures of 2, 3a, 4, 6, 7, 9a, 10a, 10b, 11, and 12 were determined by X-ray crystallography. The structures of 3a, 9a, 10a, and 10b, are related to 3, 9, and 10, respectively, by partial occupation of chloride or hydride by hydroxide. The compounds were also characterized by (1)H, (13)C, (7)Li, and (27)Al NMR and IR spectroscopy. The major conclusions from the experimental data are that a single ortho terphenyl substituent of the kind reported here are not as effective as the ligand Mes (Mes = 2,4,6-t-Bu(3)C(6)H(2)-) in preventing further coordination and/or aggregation involving the aluminum centers. In effect, one terphenyl ligand is not as successful as a Mes substituent in masking the metal through agostic and/or steric effects.     

Reactivity of the bridged-sulfide complex Pd2Cl2(μ-S)(μ-dmpm)2 toward electrophiles

The dipalladium(I) complex Pd(2)Cl(2)(dmpm)(2) (1a) [dmpm = bis(dimethylphosphino)methane] is known to react with elemental sulfur (S(8)) to give the bridged-sulfide complex Pd(2)Cl(2)(μ-S)(dmpm)(2) (2a) but, in the presence of excess S(8), PdCl(2)[P,S-dmpm(S)] (4a) and dmpm(S)(2) are generated. Treatment of 1a with elemental selenium (Se(8)), however, gives only Pd(2)Cl(2)(μ-Se)(dmpm)(2) (3a). Complex 4a is best made by reaction of trans-PdCl(2)(PhCN)(2) with dmpm(S). Complex 2a reacts with MeI to yield initially Pd(2)I(2)(μ-S)(dmpm)(2) and MeCl, and then Pd(2)I(2)(μ-I)(2)(dmpm)(2) and Me(2)S, whereas alkylation of 2a with MeOTf generates the cationic, bridged-methanethiolato complex [Pd(2)Cl(2)(μ-SMe)(dmpm)(2)]OTf (5). Oxidation of 2a with m-CPBA forms a mixture of Pd(2)Cl(2)(μ-SO)(dmpm)(2) and Pd(2)Cl(2)(μ-SO(2))(dmpm)(2), whereas Pd(2)Br(2)(μ-S)(dmpm)(2) reacts selectively to give Pd(2)Br(2)(μ-SO)(dmpm)(2) (6b). Treatment of the Pd(2)X(2)(μ-S)(dmpm)(2) complexes with X(2) (X = halogen) removes the bridged-sulfide as S(8), with co-production of Pd(II)(dmpm)-halide species. X-ray structures of 3a, 5 and 6b are presented. Reactions of dmpm with S(8) and Se(8) are clarified. Differences in the chemistry of the dmpm systems with that of the corresponding dppm systems [dppm = bis(diphenylphosphino)methane] are discussed.     

Organotransition-Metal Metallacarboranes. 46. Multidecker Sandwiches of the Cobalt Group Metals(,)(1)

The double-decker sandwich complex CpIr(2,3-Et(2)C(2)B(4)H(4)) (1a) was prepared via deprotonation of nido-2,3-Et(2)C(2)B(4)H(6) to its mono- or dianion and reaction with (CpIrCl(2))(2) in THF and isolated as a colorless air-stable solid; the B(4)-chloro derivative 1b was also obtained. Decapitation of 1a and 1b with TMEDA afforded colorless nido-CpIr(2,3-Et(2)C(2)B(3)H(5)) (2a) and its 4-chloro derivative 2b. Chlorination of 1a by Cl(2) or N-chlorosuccinimide gave the symmetrical species CpIr(2,3-Et(2)C(2)B(4)H(3)-5-Cl) (1c), which was decapped to yield nido-CpIr(2,3-Et(2)C(2)B(3)H(4)-5-Cl) (2c). The triple-decker complexes CpIr(2,3-Et(2)C(2)B(3)H(2)-4[6]-Cl)IrCp (3), an orange solid, and dark green CpIr(2,3-Et(2)C(2)B(3)H(2)-4[6]-Cl)CoCp (5) were prepared from 2a and nido-CpCo(2,3-Et(2)C(2)B(3)H(5)) (4a), respectively, by deprotonation and reaction with (CpIrCl(2))(2) in THF. Reaction of the 2c(-) anion with Rh(MeCN)(3)Cl(3) gave the dark green tetradecker complex [CpIr(Et(2)C(2)B(3)H(2)-5-Cl)](2)RhH (6). In an attempt to prepare a heterotrimetallic Co-Rh-Ir tetradecker sandwich, a three-way reaction involving the deprotonated anions derived from CpCo(2,3-Et(2)C(2)B(3)H(4)-5-Cl) (4b) and 2c with Rh(MeCN)(3)Cl(3) was conducted. The desired species CpCo(Et(2)C(2)B(3)H(2)Cl)RhH(Et(2)C(2)B(3)H(2)Cl)IrCp (7) and the tetradeckers [CpCo(Et(2)C(2)B(3)H(2)Cl)](2)RhH (8) and 6 were isolated in small quantities from the product mixture; many other apparent triple-decker and tetradecker products were detected via mass spectroscopy but were not characterized. All new compounds were isolated via column or plate chromatography and characterized via NMR, UV-visible, and mass spectroscopy and by X-ray crystal structure determinations of 1a and 3. Crystal data for 1a: space group C2/c; a = 28.890(5) ?, b = 8.511(2) ?, c = 15.698(4) ?, beta = 107.61(2) degrees; Z = 8; R = 0.049 for 1404 independent reflections having I > 3sigma(I). Crystal data for 3: space group P2(1)/c; a = 11.775(4) ?, b = 15.546(5) ?, c = 15.500(5) ?, beta = 103.16(3) degrees; Z = 4; R = 0.066 for 2635 independent reflections having I > 3sigma(I).     

High-pressure synthesis, crystal structure, and properties of BiPd2O4 with Pd2+ and Pd4+ ordering and PbPd2O4

BiPd(2)O(4) and PbPd(2)O(4) were synthesized at high pressure of 6 GPa and 1500 K. Crystal structures of BiPd(2)O(4) and PbPd(2)O(4) were studied with synchrotron X-ray powder diffraction. BiPd(2)O(4) is isostructural with PbPt(2)O(4) and crystallizes in a triclinic system (space group P1, a = 5.73632(4) ?, b = 6.02532(5) ?, c = 6.41100(5) ?, α = 114.371(1)°, β = 95.910(1)°, and γ = 111.540(1)° at 293 K). PbPd(2)O(4) is isostructural with LaPd(2)O(4) and BaAu(2)O(4) and crystallizes in a tetragonal system (space group I4(1)/a, a = 5.76232(1) ?, and c = 9.98347(2) ? at 293 K). BiPd(2)O(4) shows ordering of Pd(2+) and Pd(4+) ions, and it is the third example of compounds with ordered arrangements of Pd(2+) and Pd(4+) in addition to Ba(2)Hg(3)Pd(7)O(14) and KPd(2)O(3). In PbPd(2)O(4), the following charge distribution is realized Pb(4+)Pd(2+)(2)O(4). PbPd(2)O(4) shows a structural phase transition from I4(1)/a to I2/a at about 240 K keeping basically the same structural arrangements (space group I2/a, a = 5.77326(1) ?, b = 9.95633(2) ?, c = 5.73264(1) ?, β = 90.2185(2)° at 112 K). BiPd(2)O(4) is nonmagnetic while PbPd(2)O(4) exhibits a significant temperature-dependent paramagnetic moment of 0.46μ(B)/f.u. between 2 and 350 K. PbPd(2)O(4) shows metallic conductivity, and BiPd(2)O(4) is a semiconductor between 2 and 400 K.     

Synthesis and structural characterization of two-coordinate low-valent 14-group metal complexes bearing bulky bis(amido)silane ligands

A series of germylene, stannylene and plumbylene complexes [η(2)(N,N)-Me(2)Si(DippN)(2)Ge:] (3a), [η(2)(N,N)-Ph(2)Si(DippN)(2)Ge:] (3b), [η(2)(N,N)-Me(2)Si(DippN)(2)Sn:] (4), [η(2)(N,N)-Me(2)Si(DippN)(2)Pb:](2) (5a), and [η(2)(N,N)-Ph(2)Si(DippN)(2)Pb:] (5b) (Dipp = 2,6-iPr(2)C(6)H(3)) bearing bulky bis(amido)silane ligands were readily prepared either by the transamination of M[N(SiMe(3))(2)](2) (M = Sn, Pb) and [Me(2)Si(DippNH)(2)] or by the metathesis reaction of bislithium bis(amido)silane [η(1)(N),η(1)(N)-R(2)Si(DippNLi)(2)] (R = Me, Ph) with the corresponding metal halides GeCl(2)(dioxane), SnCl(2), and PbCl(2), respectively. Preliminary atom-transfer chemistry involving [η(2)(N,N)-Me(2)Si(DippN)(2)Ge:] (3a) with oxygen yielded a dimeric oxo-bridged germanium complex [η(2)(N,N)-Me(2)Si(DippN)(2)Ge(μ-O)](2) (6). All complexes were characterized by (1)H, (13)C, (119)Sn NMR, IR, and elemental analysis. X-ray single crystal diffraction analysis revealed that the metal centres in 3b, 4, and 5b are sterically protected to prevent interaction between the metal centre and the nitrogen donors of adjacent molecules while complex 5a shows a dimeric feature with a strong intermolecular Pb···N interaction.     

Trisilane-1,3-diolato complexes of Ti and Zr: syntheses and X-ray crystal structures

The syntheses and structures of zirconium and titanium complexes containing the novel chelating trisilane-1,3-diolate ligand [Me2Si(R2SiO)2]2- (R = SiMe3) (5)-H2 are reported. The chloride complexes [Me2Si(R2SiO)2]TiCl2 (7a) and [Me2Si(R2SiO)2]ZrCl2 x 2 THF (7b) were prepared by the reaction of MCl4 (M = Ti, Zr) with [Me2Si(R2SiO)2]2Ti (6a) and [Me2Si(R2SiO)2]2Zr (6b), which are derived from the reaction of 5 with M(NEt2)4, respectively. In the presence of TiCl4, complexes 6a and 7a undergo a ring-opening reaction to produce the dinuclear complex [Me2Si(R2SiO)2][TiCl3]2 (9). [Me2Si(R2SiO)2]TiMe2 (10) and [Me2Si(R2SiO)2]TiBnz2 (11) were prepared in moderate yields from reactions of 7a with 2 equiv of MeMgBr and BnzMgCl, respectively. According to NMR spectroscopic investigations, the reaction of the dimethyltitanium complex 10 with B(C6F5)3 led to full exchange of both methyl groups by C6F5 groups under quantitative formation of [Me2Si(R2SiO)2]Ti(C6F5)2 (12) and a mixture of B(C6F5)(3-n)Me(n), where n = 1-3. The structure of 12 is further evidenced by the preparation of an identical sample from the reaction of 7a with 2 equiv of C6F5MgBr. Refluxing an ether solution of 12 surprisingly gave [Me2Si(R2SiO)2]2TiC6F5]2O (13) as a result of ether cleavage. The structures of the complexes 7a, 7b, 9, 10, and 13 were determined by X-ray crystallography, and structural discussion of the bond parameters will be given.     

Cobalt(II) and cobalt(III) complexes of thioether-containing hexadentate pyrazine amide ligands: C-S bond cleavage and cyclometallation reaction

Anaerobic reaction of Co(O2CMe)2.4H2O with the thioether-containing acyclic pyrazine amide hexadentate ligand 1,4-bis[o-(pyrazine-2-carboxamidophenyl)]-1,4-dithiobutane (H2L1) (-CH2CH2- spacer between the two pyrazine amide tridentate coordination units) furnishes [CoII(L1)].MeOH (1a) having CoN2(pyrazine)N'2(amide)S2(thioether) coordination. It exhibits an eight-line EPR spectrum, attesting to a low-spin (S = 1/2) state of CoII. A similar reaction in air, however, furnishes [CoIII(L3a)(L3b)].2MeOH (2a) (S = 0), resulting from a C-S bond cleavage reaction triggered by an acetate ion as a base, having CoN2(pyrazine)N'2(amide)S(thioether)S'(thiolate) coordination. On the other hand, the reaction of Co(O2CMe)2.4H2O with 1,4-bis[o-(pyrazine-2-carboxamidophenyl)]-1,5-dithiopentane (H2) (-CH2CH2CH2- spacer between the two pyrazine amide tridentate coordination units) in air affords a cobalt(II) complex [CoII(L2)].MeOH (1b.MeOH) (S = 1/2); its structurally characterized variety has the composition 1b.C6H6. Interestingly, 1b.MeOH undergoes facile metal-centred oxidation by aerial O2-H2O2-[Fe(eta5-C5H5)2][PF6], which led to the isolation of the corresponding cobalt(iii) complex [CoIII(L2)][ClO4] (2b). When treated with methanolic KOH, 2b affords a low-spin (S = 0) organocobalt(III) complex [Co(III)((L2')] (3). Structures of all complexes, except 1a, have been authenticated by X-ray crystallography. A five-membered chelate-ring forming ligand L1(2-) effects C-S bond cleavage and a six-membered chelate-ring forming ligand L2(2-) gives rise to Co-C bond formation, in cobalt(III)-coordinated thioether functions due to alpha C-H bond activation by the base. A rationale has been provided for the observed difference in the reactivity properties. The spectroscopic properties of the complexes have also been investigated. Cyclic voltammetry experiments in MeCN-CH2Cl2 reveal facile metal-centred reversible-to-quasireversible CoIV-CoIII (or a ligand-centred redox process; 2a), CoIII-CoII (1a, 1b.MeOH, 2a, 2b and 3), CoII-CoI (1a, 1b.MeOH, 2aand 2b), and CoI-Co0 (1a, 1b.MeOH and 2b) redox processes.     

Flexible N,N,N-chelates as supports for iron and cobalt chloride complexes; synthesis, structures, DFT calculations and ethylene oligomerisation studies

The aryl-substituted N-picolylethylenediamine and diethylenetriamine ligands, (ArNHCH(2)CH(2))[(2-C(5)H(4)N)CH(2)]NH and (ArNHCH(2)CH(2))(2)NH (Ar = 2,6-Me(2)C(6)H(3), 2,4,6-Me(3)C(6)H(2)), have been prepared by employing palladium-catalysed N-C(aryl) coupling reactions of the corresponding primary amines with aryl bromide. Treatment of MCl(2) with (ArNHCH(2)CH(2))[(2-C(5)H(4)N)CH(2)]NH affords [[(ArNHCH(2)CH(2))((2-C(5)H(4)N)CH(2))NH]CoCl(2)](Ar = 2,6-Me(2)C(6)H(3) 1a; 2,4,6-Me(3)C(6)H(2)) 1b and [[(ArNHCH(2)CH(2))((2-C(5)H(4)N)CH(2))NH]FeCl(2)](n)(n= 1, Ar = 2,6-Me(2)C(6)H(3) 2a; n= 2, 2,4,6-Me(3)C(6)H(2) 2b) in high yield. The X-ray structures of 1a and 1b are isostructural and reveal the metal centres to adopt distorted trigonal bipyramidal geometries with the N,N,N-chelates adopting fac-structures. A facial coordination mode of the ligand is also observed in bimetallic 2b, however, in 2a the N,N,N-chelate adopts a mer-configuration with the metal centre adopting a geometry best described as square pyramidal. Solution studies indicate that mer-fac isomerisation is a facile process for these systems at room temperature. Quantum mechanical calculations (DFT) have been performed on 1a and 2a, in which the ligands employed are identical, and show the fac- to be marginally more stable than the mer-configuration for cobalt (1a) while for iron (2a) the converse is evident. Reaction of (ArNHCH(2)CH(2))(2)NH with CoCl(2) gave the five-coordinate complexes [[(ArNHCH(2)CH(2))(2)NH]CoCl(2)](Ar = 2,6-Me(2)C(6)H(3) 3a, 2,4,6-Me(3)C(6)H(2) 3b), in which the ligand adopts a mer-configuration; no reaction occurred with FeCl(2). All complexes 1-3 act as modest ethylene oligomerisation catalysts on activation with excess methylaluminoxane (MAO); the iron systems giving linear alpha-olefins while the cobalt systems give mixtures of linear and branched products.     

Syntheses and structures of heterometallic clusters by the reaction of o-carboranyl cobaltadichalcogenolato complexes

Metalladichalcogenolate cluster complexes [Cp'Co{E(2)C(2)(B(10)H(10))}]{Co2(CO)5} [Cp' = eta5-C5H5, E = S(3a), E = Se(3b); Cp' = eta5-C5(CH3)5, E = S(4a), E = Se(4b)], {CpCo[E(2)C(2)(B(10)H(10))]}(2)Mo(CO)2] [E = S(5a), Se(5b)], Cp*Co(micro2-CO)Mo(CO)(py)2[E(2)C(2)(B(10)H(10))] [E = S(6a), Se(6b)], Cp*Co[E(2)C(2)(B(10)H(10))]Mo(CO)2[E(2)C(2)(B(10)H(10))] [E = S(7a), Se(7b)], (Cp'Co[E(2)C(2)(B(10)H(10))]W(CO)2 [E(2)C(2)(B(10)H(10))] [Cp' = eta5-C5H5, E = S(8a), E = Se(8b); Cp' = eta5-C5(CH3)5, E = S(9a), E = Se(9b)], {CpCo[E(2)C(2)(B(10)H(10))]}(2)Ni [E = S(10a), Se(10b)] and 3,4-(PhCN(4)S)-3,1,2-[PhCN(4)SCo(Cp)S(2)]-3,1,2-CoC(2)B(9)H(8) 12 were synthesized by the reaction of [Cp'CoE(2)C(2)(B(10)H(10))] [Cp' = eta5-C5H5, E = S(1a), E = Se(1b); Cp' = eta5-C5(CH3)5, E = S(2a), E = Se(2b)] with Co2(CO)8, M(CO)3(py)3 (M = Mo, W), Ni(COD)2, [Rh(COD)Cl]2, and LiSCN4Ph respectively. Their spectrum analyses and crystal structures were investigated. In this series of multinuclear complexes, 3a,b and 4a,b contain a closed Co3 triangular geometry, while in complexes 5a-7b three different structures were obtained, the tungsten-cobalt mixed-metal complexes have only the binuclear structure, and the nickel-cobalt complexes were obtained in the trinuclear form. A novel structure was found in metallacarborane complex 12, with a B-S bond formed at the B(7) site. The molecular structures of 4a, 5a, 6a, 7b, 9a, 9b, 10a and 12 have been determined by X-ray crystallography.     

Synthesis and characterization of heavier dioxouranium(VI) dihalides

The synthesis and characterization of the dioxouranium(VI) dibromide and iodide hydrates, UO(2)Br(2)x3H(2)O (1), [UO(2)Br(2)(OH(2))(2)](2) (2), and UO(2)I(2)x2H(2)Ox4Et(2)O (3), are reported. Moreover, adducts of UO(2)I(2) and UO(2)Br(2) with large, bulky OP(NMe(2))(3) and OPPh(3) ligands such as UO(2)I(2)(OP(NMe(2))(3))(2) (4), UO(2)Br(2)(OP(NMe(2))(3))(2) (5), and UO(2)I(2)(OPPh(3))(2)(6) are discussed. The structures of the following compounds were determined using single-crystal X-ray diffraction techniques: (1) monoclinic, P2(1)/c, a = 9.7376(8) A, b = 6.5471(5) A, c = 12.817(1) A, beta = 94.104(1) degrees , V = 815.0(1) A(3), Z = 4; (2) monoclinic, P2(1)/c, a = 6.0568(7) A, b = 10.5117(9) A, c = 10.362(1) A, beta = 99.62(1) degrees , V = 650.5(1) A(3), Z = 2; (4) tetragonal, P4(1)2(1)2, a = 10.6519(3) A, b = 10.6519(3) A, c = 24.0758(6) A, V = 2731.7(1) A(3), Z = 4; (5) tetragonal, P4(1)2(1)2, a = 10.4645(1) A, b = 10.4645(1) A, c = 23.7805(3) A, V = 2604.10(5) A(3), Z = 4, and (6) monoclinic, P2(1)/c, a = 9.6543(1) A, b = 18.8968(3) A, c = 10.9042(2) A, beta =115.2134(5) degrees , V = 1783.01(5) A(3), Z = 2. Whereas 1 and 2 are the first UO(2)Br(2) hydrates and the last missing members of the UO(2)X(2) hydrate (X = Cl --> I) series to be structurally characterized, 4 and 6 contain room-temperature stable U(VI)-I bonds with 4 being the first structurally characterized room temperature stable U(VI)-I compound which can be conveniently prepared on a gram scale in quantitative yield. The synthesis and characterization of 5 using an analogous halogen exchange reaction to that used for the preparation of 4 is also reported.     

Reaction products of W(CO)(6) with formamidines; electronic structure of a W(2)(mu-CO)(2) core with unsymmetric bridging carbonyls

Reactions of W(CO)(6) with formamidines contrast with those of Mo(CO)(6) and Cr(CO)(6) in that the former do not yield quadruply bonded dimetal species. From the reaction of W(CO)(6) with HDAniF (HDAniF = N,N'-di-p-anisylformamidine), several new ditungsten carbonyl compounds (W(2)(mu-CO)(2)(mu-DAniF)(2)(eta(2)-DAniF)(2) (1), W(2)(mu-CO)(2)(mu-DAniF)(2)(eta(2)-DAniF)(eta(2)-CH(2)DAniF) (2), and W(2)(mu-CO)(mu-CNC(6)H(4)OCH(3))(mu-DAniF)(2)(eta(2)-DAniF)(2) (3)) have been isolated and fully characterized. In 2, CH(2)DAniF represents a DAniF ligand in which a methylene group has been added to one of the nitrogen atoms. This ligand binds to the tungsten atom using a nitrogen and a carbon atom. Compound 1 has a tungsten-tungsten bond distance of 2.476(1) A and a planar W(2)(mu-CO)(2) core structure which has C(2)(h)() symmetry with short and long W-C bond distances (1.99(1) and 2.28(1) A, respectively). DFT calculations on a model of 1 indicate that (a) the C(2)(h)() instead of D(2)(h)() symmetry of the ditungsten core may be attributed to W --> CO pi back-bonding interactions and (b) the bond between the tungsten atoms may be formulated as a double bond. The new tetragonal paddlewheel compound W(2)(DAniF)(4) (4) and the edge-sharing bioctahedron W(2)(mu-O)(mu-NC(6)H(3)Cl(2))(mu-D(Cl)PhF)(2)(eta(2)-D(Cl)PhF)(2) (5) (D(Cl)PhF = N,N'-di-(3,5-dichlorophenyl)formamidinate) have also been prepared.     

Bis[(2-diphenylphosphino)phenyl]mercury: a P-donor ligand and precursor to mixed metal-mercury (d(8)-d(10)) cyclometalated complexes containing 2-C(6)H(4)PPh(2)

Treatment of HgCl(2) with 2-LiC(6)H(4)PPh(2) gives [Hg(2-C(6)H(4)PPh(2))(2)] (1), whose phosphorus atoms take up oxygen, sulfur, and borane to give the compounds [Hg[2-C(6)H(4)P(X)Ph(2)](2)] [ X = O (3), S (4), and BH(3) (5)], respectively. Compound 1 functions as a bidentate ligand of wide, variable bite angle that can span either cis or trans coordination sites in a planar complex. Representative complexes include [HgX(2) x 1] [X = Cl (6a), Br (6b)], cis-[PtX(2) x 1] [X = Cl (cis-7), Me (9), Ph (10)], and trans-[MX(2) x 1] [X = Cl, M = Pt (trans-7), Pd (8), Ni (11); X = NCS, M = Ni (13)] in which the central metal ions are in either tetrahedral (6a,b) or planar (7-11, 13) coordination. The trans disposition of 1 in complexes trans-7, 8, and 11 imposes close metal-mercury contacts [2.8339(7), 2.8797(8), and 2.756(8) A, respectively] that are suggestive of a donor-acceptor interaction, M --> Hg. Prolonged heating of 1 with [PtCl(2)(cod)] gives the binuclear cyclometalated complex [(eta(2)-2-C(6)H(4)PPh(2))Pt(mu-2-C(6)H(4)PPh(2))(2)HgCl] (14) from which the salt [(eta(2)-2-C(6)H(4)PPh(2))Pt(mu-2-C(6)H(4)PPh(2))(2)Hg]PF(6) (15) is derived by treatment with AgPF(6). In 14 and 15, the mu-C(6)H(4)PPh(2) groups adopt a head-to-tail arrangement, and the Pt-Hg separation in 14, 3.1335(5) A, is in the range expected for a weak metallophilic interaction. A similar arrangement of bridging groups is found in [Cl((n)Bu(3)P)Pd(mu-C(6)H(4)PPh(2))(2)HgCl] (16), which is formed by heating 1 with [PdCl(2)(P(n)()Bu(3))(2)]. Reaction of 1 with [Pd(dba)(2)] [dba = dibenzylideneacetone] at room temperature gives [Pd(1)(2)] (19) which, in air, forms a trigonal planar palladium(0) complex 20 containing bidentate 1 and the monodentate phosphine-phosphine oxide ligand [Hg(2-C(6)H(4)PPh(2))[2-C(6)H(4)P(O)Ph(2)]]. On heating, 19 eliminates Pd and Hg, and the C-C coupled product 2-Ph(2)PC(6)H(4)C(6)H(4)PPh(2)-2 (18) is formed by reductive elimination. In contrast, 1 reacts with platinum(0) complexes to give a bis(aryl)platinum(II) species formulated as [Pt(eta(1)-C-2-C(6)H(4)PPh(2))(eta(2)-2-C(6)H(4)PPh(2))(eta(1)-P-1)]. Crystal data are as follows. Compound 3: monoclinic, P2(1)/n, with a = 11.331(3) A, b = 9.381(2) A, c = 14.516 A, beta = 98.30(2) degrees, and Z = 2. Compound 6b x 2CH(2)Cl(2): triclinic, P macro 1, with a = 12.720(3) A, b = 13.154(3) A, c = 12.724(2) A, alpha = 92.01(2) degrees, beta = 109.19(2) degrees, gamma = 90.82(2) degrees, and Z = 2. Compound trans-7 x 2CH(2)Cl(2): orthorhombic, Pbca, with a = 19.805(3) A, b = 8.532(4) A, c = 23.076(2) A, and Z = 4. Compound 11 x 2CH(2)Cl(2): orthorhombic, Pbca, with a = 19.455(3) A, b = 8.496(5) A, c = 22.858(3) A, and Z = 4. Compound 14: monoclinic, P2(1)/c, with a = 13.150(3) A, b = 12.912(6) A, c = 26.724(2) A, beta = 94.09(1) degrees, and Z = 4. Compound 20 x C(6)H(5)CH(3).0.5CH(2)Cl(2): triclinic, P macro 1, with a = 13.199(1) A, b = 15.273(2) A, c = 17.850(1) A, alpha = 93.830(7), beta = 93.664(6), gamma = 104.378(7) degrees, and Z = 2.     

Palladium-catalyzed coupling of allenylphosphonates, phenylallenes, and allenyl esters: remarkable salt effect and routes to novel benzofurans and isocoumarins

Coupling reactions of allenylphosphonates (OCH(2)CMe(2)CH(2)O)P(O)CH=C=CRR' [R, R' = H (1a), R = H, R' = Me (1b), R = R' = Me (1c)] with aryl iodides, iodophenol, and iodobenzoic acid in the presence of palladium(II) acetate are investigated and compared with those of phenylallenes PhCH=C=CR2 [R = H (2a), Me (2b)] and allenyl esters EtO(2)CCH=C=CR(2) [R = H (2c), Me (2d)]. While 1b and 1c couple with different stereochemical outcomes using PhI in the presence of Pd(OAc)(2)/PPh(3)/K(2)CO(3) to give phenyl-substituted 1,3-butadienes, 1a does not undergo coupling but isomerizes to the acetylene (OCH(2)CMe(2)CH(2)O)P(O)CCMe (7). In the reaction of 1c with PhI, use of K(2)CO(3) affords the butadiene (Z)-(OCH(2)CMe(2)CH(2)O)P(O)CH=C(Ph)-C(Me)=CH(2) (12); in contrast, the use of Ag(2)CO(3) leads to the allene (OCH(2)CMe(2)CH(2)O)P(O)C(Ph)=C=CMe(2) (20), showing that these bases differ very significantly in their roles. The reaction of 1a with PhI or PhB(OH)2 in (t)he presence of Pd(OAc)2/CsF/DMF leads mainly to (E)-(OCH(2)CMe(2)CH(2)O)P(O)CH=C(Me)Ph (21) and (OCH(2)CMe(2)CH(2)O)P(O)CH2-C(Ph)=CH(2) (22) and is thus a net 1,2-addition of Ph-H. Compound 1b reacts with iodophenol in the presence of Pd(OAc)(2)/PPh(3)/K(2)CO(3) to give a benzofuran that has a structure different from that obtained by using 1c under similar conditions. Treatment of 1a with iodophenol/Pd(OAc)(2)/CsF/DMF also gives a benzofuran whose structure is different from that obtained by using 2a under similar conditions. In the reaction with 2-iodobenzoic acid, 1a and 2c afford one type of isocoumarin, while 1b,c and 2a,b give a second type of isocoumarin. The structures of key compounds are established by X-ray crystallography. Utility of the phosphonate products in the Horner-Wadsworth-Emmons reaction is demonstrated.