In 1971 DuPont started the production of adiponitrile (ADN) as an intermediate in the production of Nylon(6,6). 1 This process is so far the only example of a large-scale industrial application of an alkene hydrocyanation. Originally it was developed using a monodentate phosphite-based zerovalent nickel catalyst. 2 The process consists of three steps. The hydrocyanation of butadiene leads to a mixture of 2-methyl-3-butenenitrile (2M3BN) and 3-pentenenitrile (3PN), obtained in varying ratio (typically 2:3) depending on the ligand employed. In a second step the branched 2M3BN is isomerized to the desired linear 3PN. The last step is the hydrocyanation of 3PN to ADN, requiring a Lewis acid cocatalyst such as AlCl 3 .Many efforts have been made to improve the performance of the nickel catalysts. An important step was the replacement of monodentate ligands by bidentate π-acceptor ligands that lead to higher conversion and selectivity for 3PN up to 70%. 3 A higher selectivity has been claimed only in a patent for bis(diphenylphosphino)ferrocene (DPPF) as ligand used in large excess. 4 Large bite angle ligands, based on a rigid xanthene backbone (e.g., sixantphos or thixantphos) were proven to enhance the Ni(0)-catalyst performance in hydrocyanation. 5 It was proposed that these ligands improve the reductive elimination of the product and stabilize the active Ni-species while suppressing the formation of inactive dicyano Ni(II)-complexes.Triptycene-based bidentate ligands, first described by Hofmann at al., 6 possess both a very rigid backbone and a large bite angle. So far, these systems were described only in the patent literature with examples of Rh-catalyzed hydroformylation reactions. 6,7 In more recent publications different mono-and dinuclear metal complexes with a variety of bite angles and geometries were investigated. 8 As part of our continuing interest in this field, 9 we now describe the use of a triptycene-based diphosphine ligand in the hydrocyanation of butadiene, resulting in unprecedented high selectivities to 3PN of up to 98%. A new route toward the ligand tript-PPh 2 (5) (Scheme 1) has been devised, giving considerably higher yields than the reported 6,7 method; 1,8-dichloroanthraquinone (1) was converted into the difluoro compound (2) and subsequently reduced to 1,8-difluoroanthracene (3) with Zn dust 10,11 (Scheme 1). The triptycene moiety (4) was obtained by reaction of the corresponding anthracene with benzyne, generated in situ from anthranilic acid. Nucleophilic substitution of the fluoro groups with potassium diphenylphosphide gave ligand (5) in 20% overall yield.Reaction of (5) with (cod)PtCl 2 and Ni(cod) 2 , respectively, led to the corresponding complexes (5)PtCl 2 (6) and (5)Ni(cod) (7). The pale-yellow compound 6 was characterized by means of 1 H, 13 C, and 31 P NMR spectroscopy as well as by elemental analysis.The 31 P NMR spectrum of 6 shows a singlet at δ ) 0.42 ppm with platinum satellites ( 1 J Pt-P ) 3761 Hz), suggesting that the ligand is coordinated in a cis fashion. 8c This wa...

Starting from imidazole, 1-[2-(cyclopenta-2,4-dienyl)ethyl]-3-methylimidazolium iodide (3) was obtained as a mixture of isomers by a simple three-step synthesis. The reaction of 3 with Ti(NEt2)4 or Zr(NEt2)4 by double deprotonation of the imidazolium salt led to the isomerically pure cationic complexes [{η5-C5H4-(CH2)2-NHC}M(NEt2)2]+I− (NHC = N-heterocyclic carbene) 4a (M = Ti) and 4b (M = Zr), respectively, in which a cyclopentadienyl and a methylimidazol-2-ylidene unit are linked by an ethylidene-1,2 bridge to form a novel chelating ligand system. In the case of the reaction of 3 with Zr(NEt2)4 the neutral compound [{η5-C5H4-(CH2)2-NHC}Zr(NEt2)I2] (5) is formed as an additional product. According to the X-ray structure analyses, the titanium atom of 4a is tetracoordinated while no coordinative interaction exists with the iodide anion; on the other hand, in 5 the zirconium centre is pentacoordinated.

Key indicatorsSingle-crystal X-ray study T = 294 K Mean (S-C) = 0.004 Å R factor = 0.066 wR factor = 0.138 Data-to-parameter ratio = 31.5For details of how these key indicators were automatically derived from the article, see

Crystals of 1,4,7,10-tetrathiacyclododecane silver(I) trifluoromethanesulfonate, Ag(C8H16S4)- (CF3SO3), 1,4,7,10-tetrathiacyclododecane iodo mercury(II) hexaiododimercurate(II)methylene chloride [HgI(C8H16S4)][Hg2I6] · CH2Cl2, 1,4,7,10,13,16-hexathiacyclooctadecane silver(I) trifluoromethanesulfonate [Ag(C12H24S6)](CF3SO3), 1,4,7,10,13,16-hexathiacyclooctadecane diiodocadmium, [Cd(C12H24S6)I2], and bis-3,6,9,14-tetrathiabicyclo[9.2.1]tetradeca-11-13-diene silver(I) trifluoromethanesulfonate [Ag(C10H14S4)2](CF3SO3) were obtained by reaction of solutions of the ligands and the appropriate metal salts and their X-ray crystal structures determined.