The oligomerization of ethylene produces α-olefin distributions ranging from Schulz−Flory distributions to alternating and selective oligomer distributions that can be mathematically analyzed and characterized by recurrence relations.

The synthesis and characterization of bulky diphosphine 1,2-bis(4-phosphorinone)xylene, BPX, and its palladium complexes [(BPX)PdCl 2 ] and [(BPX)Pd(O 2 CCF 3 ) 2 ] are described. BPX was evaluated as a ligand in Pd-catalyzed isomerizing methoxycarbonylation. A broad range of alkenes, including terminal, internal, branched, and functionalized alkenes, can be converted to esters with activities and selectivities matching or surpassing the performance of the state-of-the-art palladium bis(di(tert-butyl)phosphino-o-xylene (Pd-DTBPX) catalyst. A molecular structure of the precatalyst [(BPX)Pd(O 2 CCF 3 ) 2 ] was obtained showing a square planar geometry and a bite angle of 100.11(3)°. Rhodium carbonyl complexes [(BPX)Rh(CO)Cl] and [(DTBPX)Rh(CO)Cl] were synthesized to compare the relative electronic parameters, revealing a ν(CO) of 1956.8 and 1948.3 cm −1 , respectively, suggesting a reduced ability of BPX to donate electron density to the metal relative to DTBPX. Competitive protonation experiments between BPX and DTBPX in the presence of CH 3 SO 3 H exclusively produce [DTBPX(H) 2 ] 2+ , providing additional evidence that BPX is a much weaker base than DTBPX. This could be due to either the effect of the electron-withdrawing ketone group in the phosphorinone ring or the compression of the C−P−C bond angle induced by the ring structure. The 31 P NMR (CDCl 3 ) chemical shift of BPX is 5.6 ppm, upfield of DTBPX at 27.6 ppm. This anomalous result is attributed to a strong gamma substituent effect of CO in the BPX ligand. The improved activity of Pd-BPX, relative to Pd-DTBPX, could be attributed to a more electrophilic Pd II center, which could accelerate the rate-determining methanolysis step.

Tri(pyridylmethyl)phosphine (TPPh), the remarkably elusive congener of tri(pyridylmethyl)amine (TPA), has been prepared, as well as the relative tri(N-methyl-pyridylamino)phosphine (TPAMP). The coordination properties of these new ligands have been evaluated for chromium(III), iron(II), and ruthenium(II) complexes and compared with the related TPA complexes. In all cases, a different coordination behavior has been observed whereby TPPh and TPAMP always act as tridentate ligands. A chromium(III) complex [Cr(TPPh)Cl3] has been prepared, which has shown low ethylene oligomerization activity. Octahedral low spin iron(II) complexes [Fe(TPPh)2](2+) and [Fe(TPAMP)2](2+) were obtained with two ligands bound to the metal center. Ruthenium(II) chloro complexes of TPA and TPPh undergo ligand exchange reactions in acetonitrile, and the ruthenium(II) complex [Ru(MeCN)2(TPA)](2+) can be oxidized by m-CPBA in acetonitrile to give a transient ruthenium(IV) oxo complex [Ru(O)(MeCN)(TPA)](2+). Attempts to generate high valent ruthenium(IV) oxo TPPh or TPAMP complexes could not be achieved, probably due to insufficient stabilization by these strong field ligands.

A series of sterically bulky diphosphines have been prepared, including P 2 = trans-1,2-bis[(di-tertbutylphosphino)methyl]cyclohexane (4), (2-methylenepropane-1,3-diyl)bis(di-tert-butylphosphine) (5), bis[(di-tertbutylphosphino)methyl]dimethylsilane (6), and cis-and trans-11,12-bis[(di-tert-butylphosphino)methyl]-9,10-dihydro-9,10-ethanoanthracene (10 and 11). The corresponding palladium complexes of these ligands, P 2 Pd(CF 3 CO 2 ) 2 , have been synthesized and characterized. The solid-state structures of [Pd(4)(CF 3 CO 2 ) 2 ], [Pd(5)(CF 3 CO 2 ) 2 ], [Pd(6)(CF 3 CO 2 ) 2 ], and [Pd(11)(CF 3 CO 2 ) 2 ] were obtained by single-crystal X-ray diffraction and confirm the bidentate binding mode of the ligand and a square-planar coordination geometry with a minor distortion from the ideal. The diphosphines in combination with Pd(OAc) 2 have been applied in the hydroxycarbonylation of a mixture of pentenoic acid isomers to produce adipic acid with high selectivity (in several cases >95%). The (regio)selectivity of the hydroxycarbonylation reaction is highly dependent on the P 2 diphosphine ligand structure, particularly the steric bulk of the substituents on the diphosphine donor and the P−Pd−P bite angle in the complexes, with respectively tertiary alkyl phosphine substituents (tert-butyl, adamantyl) and a C4 backbone P−Pd− P bite angle >100°being the common features of highly adipic acid selective systems. It is suggested that the regioselectivity of hydroxycarbonylation becomes largely driven by the chelation of the carboxylic acid functionality of pentenoic acid substrates, when smaller size P substituents and/or when P 2 ligands with smaller bite angles (<100°) are applied.

The acid catalyzed reactive distillation of g-valerolactone yields pentenoic acids (PEAs) which can be obtained in > 90 % purity and > 97 % selectivity. The PEAs (five isomers) can be converted into a number of useful products with commercial relevance. The hydroxycarbonylation of PEAs yields adipic acid (a Nylon monomer) in very high selectivity and with good activity. Selfmetathesis of PEAs yields C6 -C8 unsaturated dicarboxylic acids which after hydrogenation produces a mixture of adipic acid, pimelic acid and suberic acid. If the PEAs are first subjected to ethenolysis; acrylic acid, 3-butenoic acid, and 4-pentenoic acid are produced. The self-metathesis of 3-butenoic acid produces b-hydromuconic acid in > 99 % selectivity which can be hydrogenated to adipic acid, whereas the self-metathesis of 4-PEA followed by hydrogenation gives suberic acid with 99 % selectivity. 3-Butenoic acid can also be hydroxycarbonylated to produce glutaric acid in 99 % selectivity.