Titanium-Catalyzed Polymerization of a Lewis Base-Stabilized Phosphinoborane.

The reaction of the Lewis base-stabilized phosphinoborane monomer tBuHPBH2 NMe3 (2 a) with catalytic amounts of bis(η5 :η1 -adamantylidenepentafulvene)titanium (1) provides a convenient new route to the polyphosphinoborane [tBuPH-BH2 ]n (3 a). This method offers access to high molar mass materials under mild conditions and with short reaction times (20 °C, 1 h in toluene). It represents an unprecedented example of a transition metal-mediated polymerization of a Lewis base-stabilized Group 13/15 compound. Preliminary studies of the substrate scope and a potential mechanism are reported.

Bidentate Phosphanyl- and Arsanylboranes.

A new class of neutral bidentate ligands with pnictogenyl-functional sites has been obtained. The reaction of tmeda⋅(BH2 I)2 (1, tmeda=tetramethylethylendiamine) with different phosphanides yields the corresponding bidentate phosphanylboranes tmeda⋅(BH2 PH2 )2 (2 a), tmeda⋅(BH2 PPh2 )2 (2 b), and tmeda⋅(BH2 tBuPH)2 (2 c). This reaction strategy could be further extended to synthesize the first bidentate arsanylborane tmeda⋅(BH2 AsPh2 )2 (3). Depending on the substituents on the phosphorus, these compounds form different AuI complexes, to build either polymeric tmeda⋅(BH2 PH2 AuCl)2 (4 a), or monomeric tmeda⋅(BH2 PPh2 AuCl)2 (4 b) products. These compounds form also neutral oligomeric group 13/15 chain-like molecules by coordination to a boron moiety such as tmeda⋅(BH2 PH2 BH3 )2 (5 a) and tmeda⋅(BH2 AsPh2 BH3 )2 (5 b). DFT calculations provide insight into the differences between the syntheses of mono- and bidentate pnictogenylboranes.

Gold(I) Complexes Containing Phosphanyl- and Arsanylborane Ligands.

The structural and photophysical properties of a series of new AuI compounds have been studied. The reactions of AuCl(tht) with the phosphanyl- and arsanylboranes RR' EBH2 NMe3 (E=P, As; R=H, Ph; R'=H, Ph, tBu) afford the complexes [AuCl(RR' EBH2 NMe3 )]. In the solid state, [AuCl(H2 PBH2 NMe3 )]2 (2 a) is a dimer showing unsupported intermolecular aurophilic interactions with short Au⋅⋅⋅Au distances. In contrast, [AuCl(H2 AsBH2 NMe3 )]n (2 b) aggregates to form 1D chains. Organic substituents on the pnictogen atoms lead to discrete molecules in [AuCl(RR' PBH2 NMe3 )] (2 c: R=H, R'=tBu; 2 d: R=R'=Ph). To increase the aurophilicity, the ionic homoleptic complexes [Au(RR' EBH2 NMe3 )2 ][AlCl4 ] (3 a-d) have been synthesized, for which 3 a,b form chains in the solid state and exhibit luminescence. The emissions show a drastic redshift with temperature decrease, correlating with decreasing Au⋅⋅⋅Au distances. DFT calculations provide insight into the bonding situation of the products.