Evaluation of P-bridged biaryl phosphine ligands in palladium-catalysed Suzuki-Miyaura cross-coupling reactions.

A family of biaryl phosphacyclic ligands derived from phobane and phosphatrioxa-adamantane frameworks is described. The rigid biaryl phosphacycles are efficient for Suzuki-Miyaura cross-coupling of aryl bromides and chlorides. In particular, coupling reactions of the challenging sterically hindered and heterocyclic substrates were viable at room temperature.

Ethylene Tetramerisation: A Structure-Selectivity Correlation.

The effect of ethylene tetramerisation ligand structures on 1-octene selectivity is well studied. However, by-product formation is less understood. In this work, a range of PNP ligand structures are correlated with the full product selectivity and with catalyst activity. As steric bulk on the N-substituent increases, the product selectivity shifts from >10 % to < 3% of both C6 cyclics and C16+ by-products. 1-Octene peaks at ca. 70%. Thereafter, only 1-hexene increases. Similar selectivity changes were observed for ortho-Ph-substituted PNP ligands. The C10-14 selectivity was less affected by the ligand structure. The ligand effect on the changes in selectivity is explained mechanistically. Lastly, an increase in ligand steric bulk was found to improve catalyst activity and reduce polymer formation by an order of magnitude. It is proposed that steric bulk promotes formation of cationic catalytic species which are responsible for selective ethylene oligomerisation.

(Biphenyl-2,2'-di-yl)di-tert-butyl-phos-phonium trifluoro-methane-sulfonate.

To aid in the elucidation of catalytic reaction mechanism of palladacycles, we found that reaction of trifluoro-methane-sulfonic acid with a phosphapalladacycle resulted in elimination of the palladium and formation of the title phospholium salt, C20H26P(+)·CF3SO3(-). Selected geometrical parameters include P-biphenyl (av.) = 1.801 (3) Šand P-t-Bu (av.) = 1.858 (3) Å, and significant distortion of the tetra-hedral P-atom environment with biphen-yl-P-biphenyl = 93.93 (13)° and t-Bu-P-t-Bu = 118.82 (14)°. In the crystal, weak C-H⋯O inter-actions lead to channels along the c axis that are occupied by CF3SO3(-) anions.

Di-µ-chlorido-bis-{[2-(di-tert-butyl-phosphan-yl)biphenyl-3-yl-κ(2)C(3),P]palladium(II)} dichloro-methane disolvate.

The asymmetric unit of the title compound, [Pd(2)Cl(2)(C(20)H(26)P)(2)]·2CH(2)Cl(2), contains one half-mol-ecule of the palladium complex and a dichloro-methane solvent mol-ecule. In the complex, two Pd(II) atoms are bridged by two Cl atoms, with the other two coordination sites occupied by a C atom of the biphenyl system and a P atom, resulting in a distorted square-planar coordination geometry of the Pd(II) atom and a cyclo-metallated four-membered ring. The Pd(2)Cl(2) unit is located about an inversion center. The planes of the rings of the biphenyl system make a dihedral angle of 66.36 (11)°.

Bis[(1,1'-biphenyl-2,2'-di-yl)di-tert-butyl-phospho-nium] di-µ-chlorido-bis-[dichlorido-palladate(II)].

In the title compound, (C(20)H(26)P)(2)[Pd(2)Cl(6)], the Pd(II) atom within the hexachloridodipalladate(II) dianion has a square-planar geometry. It resides on a centre of inversion with the asymmetric unit containing half of the dianion and one phospho-nium cation. Only weak C-H⋯π inter-actions are present in the crystal structure.

(Acetato-κ(2)O,O')[2'-(di-tert-butyl-phosphanyl)-1,1'-biphenyl-κ(2)P,C(2)]palladium(II).

The structure of the title compound, [Pd(C(2)H(3)O(2))(C(20)H(26)P)], shows a distorted square-planar geometry for the Pd(II) atom, with significant deviations being evident owing to the asymmetric coordination mode of the acetate ligand. A weak intra-molecular C-H⋯O inter-action is noted. The crystal studied was a racemic twin.

µ-Carbonato-κ(4) O,O':O',O''-bis-{[2'-(di-tert-butyl-phosphan-yl)biphenyl-2-yl-κ(2) P,C (1)]palladium(II)} dichloro-methane monosolvate.

The title compound, [(µ2-CO3){Pd(P(t-C4H9)2(C12H8)}2]·CH2Cl2, the first CO3-bridged palladium dimer complex reported to date, was obtained while preparing the Pd(0) complex with (2-biphen-yl)P( (t) Bu)2. In the crystal, each palladium dimer is accompanied by a dichloro-methane solvent mol-ecule. Coordination of the carbonate and chelated phosphane ligands gives distorted square-planar environments at the Pd atoms. Important geometrical parameters include Pd-P(av.) = 2.2135 (4) Å, Pd-C(av.) = 1.9648 (16) Šand P-Pd-C = 84.05 (5) and 87.98 (5)°, and O-Pd-O' = 60.56 (4) and 61.13 (4)°. Bonding with the carbonate O atoms shows values of 2.1616 (11) and 2.1452 (11) Šfor the Pd-O-Pd bridge, whereas other Pd-O distances are slightly longer at 2.2136 (11) and 2.1946 (11) Å. One of the tert-butyl groups is disordered over two set of sites with an occupancy ratio of 0.723 (6):0.277 (6). Weak C-H⋯O interactions are observed propagating the molecules along the [100] direction.

trans-Bis[bis-(2-methoxy-phen-yl)phenyl-phosphine-κP]dichloridopalladium(II).

The structure of the title compound, [PdCl(2)(C(20)H(19)O(2)P)(2)], shows a square-planar geometry for the Pd(II) ion within a Cl(2)Pd[PPh(PhOMe)(2)](2) ligand set. The Pd(II) atom sits on an inversion centre and therefore the asymmetric unit contains the Pd(II) atom, one Cl atom and one bis-(2-methoxy-phen-yl)phenyl-phosphine ligand. The trans arrangement of ligands is also imposed by symmetry.

trans-Dichloridobis[tris-(2-methoxy-phen-yl)phosphine]palladium(II).

The structure of the title compound, [PdCl(2)(C(21)H(21)O(3)P)(2)], shows a nearly square-planar geometry for the Pd(II) atom within the Cl(2)Pd[P(PhOMe)(3)](2) ligand set. The Pd(II) atom sits on a centre of inversion and therefore the asymmetric unit contains one half-mol-ecule, i.e. half of one Pd(II) atom, one Cl atom and one tris-(2-methoxy-phen-yl)phosphine ligand.

trans-Dichloridobis[tris-(4-methoxy-phen-yl)phosphine]palladium(II) benzene monosolvate.

The structure of the title compound, [PdCl(2)(C(21)H(21)O(3)P)(2)]·C(6)H(6), shows a square-planar geometry for the Pd(II) atom within a Cl(2)[P(PhOMe)(3)](2) ligand set. The crystal structure contains benzene as solvent. The Pd(II) atom sits on a centre of inversion and therefore the asymmetric unit contains the Pd(II) atom, one Cl atom, one tris-(4-methoxy-phen-yl)phosphine ligand and one half of the benzene solvent mol-ecule.

Furanoterpenoids from Siphonochilus aethiopicus.

Two new furanoterpenoid derivatives, namely 4a alpha H-3,5 alpha,8 alpha beta-trimethyl-4,4a,9-tetrahydro-naphtho[2,3-b]-furan-8-one and 2-hydroxy-4a alpha H-3,5 alpha, 8a beta-trimethyl-4,4a,9-tetrahydronaphtho[2,3-b]-furan-8-one, were isolated from Siphonochilus aethiopicus, a member of the family Zingiberaceae. Their structures were elucidated using high field NMR techniques.