Cory A. Jaska

Rhodium-catalyzed formation of boron–nitrogen bonds: a mild route to cyclic aminoboranes and borazines

Secondary amine–borane adducts R2NH·BH3, which are stable to H2 elimination below 100 °C, undergo efficient catalytic dehydrocoupling at 25–45 °C in the presence of RhI or RhIII complexes to quantitatively form cyclic aminoboranes [NR2–BH2]2 (1: R = Me or 2: cyclo-C4H8); under similarly mild conditions, the analogous adducts NH3·BH3 and MeNH2·BH3 yield borazines [RN–BH]3 (3: R = H or 4: R = Me) in yields limited by intermolecular coupling reactions.

Chemistry of phosphine–borane adducts at platinum centers: dehydrocoupling reactivity of Pt( ii ) dihydrides with P–H bonds

The reaction of the Pt(II) dihydride complex cis-[PtH2(dcype)](dcype = 1,2-bis(dicyclohexylphosphino)ethane) with the primary or secondary phosphine-borane adducts PhRPH x BH3(R = H, Ph) was found to exclusively afford the mono-substituted complexes cis-[PtH(PPhR x BH3)(dcype)](1: R = H; 2: R = Ph)via a dehydrocoupling reaction between Pt-H and P-H bonds. Similar reactivity was observed between the uncoordinated phosphines PhRPH (R = H, Ph) and cis-[PtH2(dcype)], which gave cis-[PtH(PPhR)(dcype)](4: R = H; 5: R = Ph). The complexes were characterized by 1H, 11B, 13C and 31P NMR spectroscopy, IR, MS and, in the case of 2, X-ray crystallography that confirmed the cis geometries. The di-substituted complex cis-[Pt(PhPH x BH3)2(dcype)](3) was prepared from the reaction of cis-[PtCl2(dcype)] with two equivalents of Li[PPhH x BH3]. This suggested that steric reasons alone cannot be used to explain the lack of reactivity with respect to a second dehydrocoupling reaction involving the remaining Pt-H bond in complexes 1, 2, 4 and 5.

Metal-catalyzed routes to rings, chains and macromolecules based on inorganic elements

This Perspective discusses the application of transition metal-catalyzed reactions to the formation of rings, oligomeric chains and macromolecules based on p-block and d-block elements. For example, the catalytic dehydrocoupling of Group 13–Group 15 Lewis acid–Lewis base adducts (e.g. 1° or 2° phosphine–boranes or amine–boranes) has been shown to yield high molecular weight polyphosphinoboranes, cyclic aminoborane species or borazines. The metal-catalyzed ring-opening polymerization (ROP) of silicon-bridged [1]ferrocenophanes allows molecular weight control through the use of silane capping agents, and permits the synthesis of block copolymers via the use of reactive polymer end-groups.

CATALYTIC DEHYDROCOUPLING OF AMINE-BORANE ADDUCTS TO FORM AMINOBORANES AND BORAZINES

A mild, catalytic dehydrocoupling route to aminoboranes and borazine derivatives from either primary or secondary amine-borane adducts has been developed using late transition metal complexes as precatalysts. The dehydrocoupling of Me 2 NH·BH 3 was found to be catalyzed by 0.5 mol% [Rh(1,5-cod)(μ-Cl)] 2 in solution at 25°C to give [Me 2 N─BH 2 ] 2 (1) quantitatively after ca. 8 h. This new catalytic method was extended to other secondary adducts RR ′NH·BH 3 which afforded the dimeric [(1,4-C 4 H 8 )N─BH 2 ] 2 (2) and [PhCH 2 (Me)N─BH 2 ] 2 (3) or the monomeric aminoborane i Pr 2 N═BH 2 (4) under mild conditions. The catalytic dehydrocoupling of NH 3 ·BH 3 , MeNH 2 ·BH 3 , and PhNH 2 ·BH 3 at 45°C affords the borazine derivatives [RN─BH] 3 (5: R = H; 6: R = Me; 7:R = Ph). TEM analysis of the contents of the reaction solution for the [Rh(1,5-cod)(μ-Cl)] 2 catalyzed dehydrocoupling of Me 2 NH·BH 3 together with Hg poisoning experiments suggested a soluble heterogeneous catalyst involving Rh(0) nanoclusters.

METAL-CATALYZED ROUTES TO RINGS, CHAINS, AND MACROMOLECULES BASED ON INORGANIC ELEMENTS

In this perspective article, some of our recent work directed at the development of new catalytic routes to rings, chains, and macromolecules based on main group and transi- tion elements will be discussed.

Metal-catalyzed routes to rings, chains, and macromolecules based on inorganic elements

In this perspective article, some of our recent work directed at the development of new catalytic routes to rings, chains, and macromolecules based on main group and transition elements will be discussed.

Synthesis and novel reactivity of platinum phosphine–borane complexes trans-[PtH(PPhR·BH3)(PEt3)2] (R = H, Ph)

The oxidative-addition reaction of Pt(PEt3)3 with the phosphine–borane adducts PhPH2·BH3 and Ph2PH·BH3 leads to regioselective insertion of the Pt(PEt3)2 fragment into the P–H bond to afford the hydride complexes trans-[PtH(PPhR·BH3)(PEt3)2 ] (R = H 1, R = Ph 2); reaction of 2 with PhPH2·BH3 leads to an unusual ligand exchange reaction which generates 1 and Ph2PH·BH3.