Ulli Englert

SYNTHESIS AND STRUCTURE OF THE FIRST TERMINAL BORYLENE COMPLEXES

A nearly linear arrangement is observed for the three atoms in the central W-B-N unit of the tungsten complex [(CO)5 WBN(SiMe3 )2 ] (1) in the crystal (W-B-N 177.9°; see picture). This compound along with its Cr analogue represent the first examples of terminal borylene complexes with a two-coordinate metal-bound boron atom. The geometries of the axial and equatorial CO groups in 1 are similar, and thus indicate that there is no trans effect of the borylene ligand.

Synthese und Struktur der ersten terminalen Borylenkomplexe

Nahezu linear sind die drei Atome der zentralen W-B-N-Einheit des Wolframkomplexes [(CO)5WBN(SiMe3)2] 1 im Kristall angeordnet (Bindungswinkel 177.9°; siehe Bild). Diese Verbindung und ihr Cr-Analogon sind die ersten terminalen Borylenkomplexe mit zweifach koordiniertem Bor. Die ahnliche Geometrie des axialen und der aquatorialen CO-Liganden in 1 spricht gegen einen trans-Effekt des Borylenliganden.

Main-chain boron-containing oligophenylenes via ring-opening polymerization of 9-H-9-borafluorene.

9-H-9-Borafluorene (H(8)C(12)BH; 5) can be generated in situ from 9-Br-9-borafluorene and Et(3)SiH in benzene or hexane. Monitoring of the reaction by NMR spectroscopy at rt in C(6)D(6) reveals that 5 forms C(1)-symmetric dimers (5)(2) under these conditions. DFT calculations on conceivable isomers of (5)(2) and a comparison of calculated and experimentally determined (1)H, (13)C, and (11)B NMR shift values lead to the conclusion that (5)(2) is not a classical dimer H(8)C(12)B(μ-H)(2)BC(12)H(8), but contains one B-H-B three-center, two-electron bond together with a boron-bridging phenyl ring. Addition of 1 equiv of pyridine to (5)(2) leads to the clean formation of the pyridine adduct H(8)C(12)BH(py) (5·py). Likewise, (5)(2) can be employed in hydroboration reactions, as evidenced by its transformation with 0.5 equiv of tert-butylacetylene, which gives the hydroboration products tBuC(H)(2)C(H)(BC(12)H(8))(2) (9) and tBuC(H)C(H)BC(12)H(8) in almost quantitative yield. (5)(2) is not long-term stable in benzene solution. Addition of pyridine to aged reaction mixtures allowed the isolation of the adduct (py)H(2)B-C(6)H(4)-C(6)H(4)-(py)BC(12)H(8) (10·py(2)) of a ring-opened dimer of 5. Storage of a hexane solution of 9-Br-9-borafluorene and Et(3)SiH for 1-2 weeks at rt leads to the formation of crystals of a ring-opened pentamer H[-(H)B-(C(6)H(4))(2)-](4)BC(12)H(8) (11) of 5 (preparative yields are obtained after 1-4 months). The polymer main chain of 11 is reinforced by four intrastrand B-H-B three-center, two-electron bonds. Apart from the main product 11, we have also isolated minor amounts of closely related oligomers carrying different chain ends, i.e., H(8)C(12)B-(C(6)H(4))(2)[-(H)B-(C(6)H(4))(2)-](2)BC(12)H(8) (12) and H[-(H)B-(C(6)H(4))(2)-](5)BH(2) (13). When the reaction between 9-Br-9-borafluorene and Et(3)SiH is carried out in refluxing toluene, the cyclic dimer [-(μ-H)B-(C(6)H(4))(2)-](2) (14) can be obtained in a crystalline yield of 25%. The compounds 9, 10·py(2), 11, 12, 13, and 14 have been structurally characterized by X-ray crystallography. The entire reaction pathway leading from 5 to 10, 11, 12, 13, and 14 has been thoroughly elucidated by DFT calculations and we propose a general mechanistic scenario applicable for ring-opening polymerization reactions of 9-borafluorenes.

Structural trends in one and two dimensional coordination polymers of cadmium(II) with halide bridges and pyridine-type ligands

Cadmium dihalides were reacted with pyridine derivatives as Lewis bases, and the solid state structures of 15 reaction products were studied by X-ray diffraction; all but one of these structures are reported for the first time. Among the 15 complexes there are 13 coordination polymers containing six-coordinated cadmium with four bridging halides in the equatorial and two pyridine ligands in the axial positions of a pseudo octahedron. For unidentate ligands such as pyridine and 3-chloro-, bromo- or methylpyridine chain polymers of composition [CdX2(L)2]1∞ were formed. The six combinations of Cl, Br, or I as bridging halides with 3-halopyridine and the two of chloride and bromide bridges with 3-methylpyridine lead to eight isomorphous compounds in the space group P21/c. In a second structure type 4,4′-bipyridyl was used to link neighbouring chains to two-dimensional nets with [CdX2(bpy)]2∞ stoichiometry. The chloro and bromo derivatives are isomorphous and crystallise in a space group Pban whereas the iodide bridged complex was obtained in the supergroup Cmmm. The halogen substituted pyridines represent the most versatile ligands for the formation of coordination polymers—they can be accommodated in the whole range of halide bridged [M(μ-X)2]1∞ chains (M = Zn, Cd) covering metal⋯metal distances between 3.654 and 4.143 A. In contrast to the above mentioned halide bridged topologies terminal rather than bridging iodide ligands occur in [CdI2(py)2] and [CdI2(3-Mepy)2]: these complexes are mononuclear with the metal center in tetrahedral coordination.

Synthesis, characterisation and catalytic activity of Pd(II) and Ni(II) complexes with new cyclic α-diphenylphosphino-ketoimines. Crystal structure of 2,6-diisopropyl-N-(2-diphenylphosphino-cyclopentylidene)aniline and of 2,6-diisopropyl-N-(2-diphenylphosphino-cyclohexylidene)aniline

Abstract New cyclic α-diphenylphosphino-ketoimines have been synthesised by deprotonation of the corresponding imine and subsequent reaction with chlorodiphenylphosphine. The crystal structures of two of these compounds containing a cyclopentylidene and cyclohexylidene backbone are discussed. Reaction of these bidentate phosphorus–nitrogen (P∧N) ligands with (cod)Pd(CH3)Cl leads to neutral complexes of the general formula (P∧N)Pd(CH3)Cl which have been reacted with AgSbF6 to yield cationic complexes of formula [(P∧N)Pd(CH3)(NCCH3)]SbF6. Reaction of these ligands with (1,2-dimethoxyethane)NiBr2 yields neutral nickel(II) complexes that have been characterised by IR and elemental analysis. Cationic Pd(II) complexes as well as MAO-activated neutral nickel(II) complexes have been used as ethylene oligomerisation catalysts. The cationic palladium(II) complexes show a marked pressure dependence of TOF, with α-olefin fraction and Schulz-Flory α-values explainable in the light of the accepted mechanism for analogous complexes. By increasing the steric bulkiness of the substituent on the imine, or by using ligands with cyclohexylidene or cycloheptylidene backbone instead of cyclopentylidene, a drop in catalytic activity is observed. Nickel(II) complexes of the title ligands activated with MAO permit to confirm the latter conclusions. In comparison with palladium their use brings to comparable linearities but higher oligomerisation grades as well as α-olefin fraction. Cationic palladium(II) complexes are also active in the propene and 1-butene oligomerisation.

Asymmetric hydrovinylation of styrene applying cationic allyl palladium complexes of a P-chiral ligand

Abstract Cationic allyl palladium complexes of the diasteriomerically pure P-chiral ligand tert-butyl(menthyl-O)phenylphosphinite 1 were prepared from [(η3-C3H5)PdI]2 and [(η3-C3H5)Pd(cod)]X. Ligand 1 and the complex [(η3-C3H5)PdI(1)] 9 were characterized by X-ray crystallography. The absolute configuration at the phosphorus center of 1 was determined to be (S) for the (−)-menthol derivative. Crystals are orthorombic, space group P212121, a=8.505(3) A, b=10.82(1) A, c=23.297(3) A, V=2144(2) A3. Complex 9 shows distorted square planar geometry. Crystals are trigonal, space group P32, a=13.980(5) A, c=11.292(3) A, V=1911(2) A3. Asymmetric codimerization of styrene and ethylene was successfully applied. High enantioselectivities of up to 86% ee have been obtained at room temperature. The codimer 3-phenylbut-1-ene (3PB1) was formed in high selectivity (up to 96%) with only small amounts of the isomerization products E- and Z-2-phenylbut-2-ene. By addition of various coordinating solvents, the catalyst system was efficiently stabilized. Variation of the complex counter anion had significant effect on enantioselectivity.

Novel Cr-PNP complexes as catalysts for the trimerisation of ethylene

Cr(III) complexes of tridentate PNP ligands have been prepared and evaluated as catalysts for ethylene trimerisation, with several giving high activity and excellent selectivity towards 1-hexene when activated with methylaluminoxane.

Synthesis and characterization of homologous nickel(II) and palladium(II) complexes with biphosphine monoxide ligands Ph2P(CH2)nP(O)Ph2 (n = 1–3) and pTol2P(CH2)P(O)pTol2

Abstract A series of cationic nickel complexes [(η3-methally)Ni(P∧P(O))]SbF6 (1–4) [P∧P(O) = Ph2P(CH2)P(O)Ph2 (dppmO) (1), Ph2P(CH2)2P(O)Ph2 (dppeO) (2), Ph2P(CH2)3P(O)Ph2 (dpppO) (3), pTol2P(CH2)P(O)pTol2 (dtolpmO) (4)] has been synthesized in good yields by treatment of [(η3-methally)NiBr]2 with biphosphine monoxides and AgSbF6. The ligands are coordinated in a bidentate way. Starting from [(η3-all)PdI]2 the cationic complexes [(η3-all)P∧P(O))]Y (8–14). [P∧P(O) = dppmO, dppeO, dpppO, dtolpmO;Y = BF4, SbF6, CF3SO3, pTolSO3] were synthesized in good yields. The coordination mode of the ligand is dependent on the backbone and the anion, revealing a monodentate coordination with dppmO for stronger coordinating anions. The intermediates [(η3-all)Pd(I)(P∧P(O)-κ1-P)] (5–7) [P∧P(O) = dppmO (5), dppeO (6), dtolpmO (7)] were isolated and characterized. Neutral methyl complexes [(Cl)(Me)Pd(P∧P(O))] (15–18). [P∧P(O) = dppmO (15), dppeO (16), dpppO (17), dtolpmO (18)] can easily be obtained in high yields starting from [(cod)PdCl2]. For dppmO two different routes are presented. The structure of [(Me)(Cl)Pd{;Ph2P(CH2-P(O)Ph2-κ2-P,O};] · CH2Cl2 (15) with the chlorine atom trans to phosphorus was determined by X-ray diffraction.

Bimetallic Coordination Polymers via Combination of Substitution-Inert Building Blocks and Labile Connectors

A rational approach to the synthesis of silver-chromium mixed-metal coordination polymers is presented: 3-cyanoacetylacetone (HacacCN) features two potential binding sites. After deprotonation, it has been used as a chelating dionato ligand in the pseudo octahedral complex Cr(acacCN) 3; two polymorphs of this compound have been identified. In its protonated form, HacacCN was employed as a N donor toward Ag(I). Both functionalities may be exploited within the same solid: The chromium complex and silver salts of weakly coordinating anions have been successfully combined to mixed-metal coordination polymers. Cr(acacCN) 3 plays the role of a substitution-inert tecton with predictable bonding geometry which interacts with the conformationally soft silver cations via two or all three of its peripheric nitrile groups. From an equimolar amount of both constituents, six solids featuring a 1:1 ratio between Cr- and Ag-derived building blocks were obtained in good yield; their structures depend on the counteranions and the cocrystallized solvent and correspond either to 2D networks with (6,3) or augmented (4,4) topology or, in one case, adopt a 3D connectivity. In addition, three products with a Cr/Ag = 2:1 stoichiometry have been isolated: they adopt two-dimensional network structures.

BORYL- AND BRIDGING BORYLENEIRON COMPLEXES FROM AMINODICHLOROBORANES

Depending on the nature of the amino group bound to the boron atom, the reactions of various aminodichloroboranes R2NBCl2 with Na[(η5-C5R′5)Fe(CO)2] yield either boryl or bridging borylene complexes of iron. The compounds [(C5R′5)(CO)2Fe{BCl(NR2)}] (1a, C5R′5 = C5H5, R = Me; 1b, C5R′5 = C5H4Me, R = Me; 1c, C5R′5 = C5Me5, R = Me) and [(η-BNR2)(μ-CO){(C5R′5)Fe(CO)}2] (2a, C5R′5 = C5H5, R = SiMe3; 2b, C5R′5 = C5H4Me, R = SiMe3) were isolated as orange (1a−c) or red (2a, b) crystalline solids, and characterized by multinuclear NMR methods and IR spectroscopy. The structures of 1c and 2b in the crystalline state were determined by single-crystal X-ray studies.