Soluble B À N Polymers DOI: 10.1002/anie.200803089 Soluble Boron–Nitrogen High Polymers from Metal- Complex-Catalyzed Amine Borane Dehydrogenation** Vincent Pons and R. Tom Baker* In memory of Clinton F. Lane boron · dehydrocoupling · homogeneous catalysis · nitrogen · polymers Over the last few decades, catalytic dehydrocoupling has evolved from a mechanistically interesting chemical trans- formation [1, 2] to a practical route to inorganic polymers that have shown utility as new materials and processable ceramic precursors. [3] In attempting to make new boron–phosphorous and boron–nitrogen inorganic polymers, Manners and co- workers studied the heteronuclear dehydrocoupling of phos- phine boranes and amine boranes. While the former gave high-molecular-weight polymers such as (PhHP À BH 2 ) n , [4] evaluation of a variety of catalysts with primary and secondary amine boranes or even ammonia borane lead only to B ÀN cyclic oligomers. [5] However, using an iridium phosphinito pincer complex originally employed by Gold- berg, Heinekey, and co-workers [6] for dehydrogenation of ammonia borane (AB, H 3 N À BH 3 ), Manners and co-workers now report formation of soluble aminoborane polymers and copolymers derived from primary amine boranes (Scheme 1). [7] With this report, an analogy is made between primary aminoboranes, RHNBH 2 , and a-olefins. The high selectivity obtained by the authors contrasts with that found in previous reports on thermal and metal-catalyzed amine borane dehydrogenation. [8] The prospects of tuning metal complex catalysts for control of B ÀN polymer microstructure are exciting for synthesis of new B ÀN materials. Moreover, variation of the substituents at the nitrogen atom of the primary amine borane offers promise for processable pre- cursors to carbon-free B À N ceramics. The chemistry of amine boranes, which began in earnest in the mid twentieth century, [9] continues to attract chemists and materials scientists. Organic chemists have exploited the reducing and hydroborating properties of amine boranes as convenient alternatives to the air- and moisture-sensitive borane–THF adduct and borohydride salts. Although amine boranes are usually less reactive, mild reaction conditions are permitted by use of metal amidoboranes [10] or transition- metal catalysts [11] for reactions such as the reduction of olefins, amides, or epoxides. For example, while hydrobora- tion of alkenes using tBuH 2 N À BH 3 proceeds only at higher temperature, Couturier and co-workers demonstrated trans- fer hydrogenation at 25 8C using 10 mol% Pd/C. [12] More recently, Jiang and Berke proposed a mechanism for the dehydrocoupling of dimethylamine borane (DMAB, Me 2 HNÀBH 3 ) and subsequent olefin transfer hydrogenation by homogeneous rhenium catalysts. [13] In materials science applications, Stucky and co-workers showed that changing the amine group of the amine borane could be used to control both nucleation and growth rate of dodecanethiol-capped gold nanoparticles. [14] This work takes advantage of a tunable borane reducing agent for nano- particle growth control that will certainly see more applica- tion. Initial studies of AB thermolysis detailed the preparation of (H 2 N À BH 2 ) n for which a linear structure was first proposed primarily on the basis of X-ray powder diffraction data. [15] While early reports of insoluble aminoborane polymers date from 1938, [16] later application of a battery of modern techniques (X-ray diffraction, IR, XPS, and MAS NMR spectroscopy as well as mass spectrometry) has not yet been able to distinguish between linear and large cyclic oligom- ers. [17, 18] In pursuit of processable B ÀN ceramic precursors, Blum et al. described the first example of transition-metal-catalyzed dehydrogenation of amine boranes. [19] Heating a benzene Scheme 1. Diverse products derived from metal-catalyzed amine bor- ane dehydrogenation. cod = 1,5-cyclooctadiene, pocop = k 3 -1,3-(OPt- Bu 2 ) 2 C 6 H 3 . [*] Dr. V. Pons, Dr. R.T. Baker Chemistry Division, Los Alamos National Laboratory MS J582, Los Alamos, NM 87507 (USA) Fax: (+ 1) 505-667-9905 E-mail: bakertom@lanl.gov [**] We thank Prof. L. G. Sneddon and Prof. R. T. Paine for helpful discussions. Highlights 9600  2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2008, 47, 9600 – 9602