COMMUNICATIONS DOI: 10.1002/adsc.200900713 Highly Linear-Selective Hydroformylation of 1-Alkenes using Formaldehyde as a Syngas Substitute Gouki Makado,a Tsumoru Morimoto,a,* Yasuko Sugimoto,a Ken Tsutsumi,a Natsuko Kagawa,b and Kiyomi Kakiuchia a Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), Takayama, Ikoma, Nara 630-0192, Japan Fax : (+81)-743-72-6081; e-mail: [email protected] b Department of Medicinal Organic Chemistry, Chiba University Yayoi, Inage, Chiba 263-8522, Japan Received: October 14, 2009; Revised: November 30, 2009; Published online: February 9, 2010 Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.200900713. Abstract: A highly linear-selective hydroformyla- appeared regarding the use of paraformaldehyde in tion of 1-alkenes using formaldehyde without the hydroformylation reactions without the direct use of direct use of syngas is described. One rhodium(I) syngas,[4,5,6] although they have not yet afforded syn- complex catalyzes two processes in the overall hy- thetically useful levels of productivity and regioselec- droformylation of 1-alkenes using formaldehyde as tivity.[7] The method using formaldehyde consists of the syngas substitute to give hydroformylated alde- two cooperative catalytic processes: the catalytic de- hydes with excellent regioselectivities. A high regio- carbonylation of formaldehyde to give a carbonyl selectivity (linear/branched=up to 98/2) and chemi- moiety and hydrogen, and their use in the subsequent cal yield (up to 95%) can be achieved by the simul- hydroformylation of alkenes. Regardless of the com- taneous use of two types of phosphanes as ligands. plexity involved in the overall catalysis, the aforemen- tioned reports have used only a single catalyst for the Keywords: alkenes; formaldehyde; homogeneous two different processes. It is, however, possible that catalysis; hydroformylation; rhodium two discrete catalysts could be used in the decarbony- lation and hydroformylation processes. Herein we wish to report on a highly selective, highly efficient hydroformylation without the direct use of syngas by using two different types of catalysts, which are suita- Hydroformylation involves the addition of carbon ble for each process. monoxide and hydrogen (CO/H2, syngas) to alkenes In order to simultaneously generate two types of in the presence of a transition metal catalyst to give rhodium catalysts in one reaction system, we adopted homologous linear (l) and/or branched (b) alde- a strategy in which two different rhodium species are hydes.[1] Because of its versatility, it represents syn- generated in situ by adding two phosphanes to a thetic routes to various aldehydes that are useful in a single rhodium complex. For the success of the strat- wide range of areas from fine and specialty chemicals egy, it is essential that the decarbonylation process is production to pharmaceuticals synthesis.[2] Since the controlled by one phosphane more strongly than the discovery of the reaction by Roelen in 1938,[3] consid- other and that the hydroformylation process is re- erable efforts have been devoted to the development versed. BINAP was a promising candidate as an effec- of new catalysts including new ligands and the utiliza- tive ligand for a rhodium catalyst in the decarbonyla- tion of novel reaction media, such as the use of an tion process, because it is known that the rhodium aqueous biphase, supercritical carbon dioxide, fluo- complex having BINAP is a more efficient catalyst rous biphase, or ionic liquids, in attempts to improve for the decarbonylation of aldehydes than xantphos.[8] the efficiency and selectivity (regio- and enantioselec- In addition, we also have recently reported that the tivity) of the reaction. A recent innovation in this use of BINAP ligand facilitates a rhodium(I)-cata- chemistry involves the development of a protocol lyzed CO gas-free carbonylation reaction using para- using formaldehyde (HCHO) as a syngas substitute. formaldehydeACHTUNGRE as the CO substitute.[5e] Towards a re- This promises to be an experimentally convenient al- gioselective hydroformylation process, we selected ternative to the transformation. Some reports have xantphos, which is a representative ligand for the ex- Adv. Synth. Catal. 2010, 352, 299 – 304 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 299 COMMUNICATIONS Gouki Makado et al. tremely highly linear-selective hydroformylation cata- Next, we investigated the effect of BINAP or xant- lyzed by a rhodium complex.[9] phos on the efficiency and selectivity of hydroformy- We initially carried out the rhodium-catalyzed hy- lation using syngas. Using BINAP and/or xantphos as droformylation reaction of 1-decene (1) with formalin ligand(s), the turnover frequency (TOF) in the early under the catalytic conditions consisting of [RhCl- stage (1 h) of the hydroformylation of 1-decene (1) ACHTUNGRE (cod)]2, BINAP, and xantphos: 1 (1 mmol), formalin with atmospheric syngas was examined: 1-decene ACHTUNGRE (0.37 mL of 37 wt% aqueous solution, 5 mmol equiva- (1 mmol), [RhCl(cod)]2 (0.005 mmol), and phos- ACHTUNGRE lents to formaldehyde), [RhCl(cod)]2 (0.01 mmol), phane(s) (0.02 mmol) in toluene (6 mL) under atmos- BINAP (0.02 mmol), xantphos (0.02 mmol) in toluene pheric syngas (CO/H2 =1/1) at 90 8C for 1 h. When (6 mL) at 90 8C for 20 h. The reaction proceeded with only BINAP was used as a ligand, linear (2-l) and an extremely high regioselectivity to give the linear branched (2-b) aldehydes were formed in a ratio of 2- aldehyde 2-l and the branched aldehyde 2-b in 80% l/2-b= 65/35 (TOF= 3.05 hÀ1). When only xantphos yield in a ratio of 2-l/2-b=97/3, along with 18% of was used, the reaction proceeded much more smooth- isomers of 1-decene (Table 1, entry 1).[10] In contrast, ly (TOF= 19.9 hÀ1) to give these aldehydes with a the use of BINAP or xantphos resulted in a low selec- high linear-selectivity of 2-l/2-b =93/7. Furthermore, tivity or a low efficiency (entries 2 and 3). These re- the use of a combination of BINAP (0.01 mmol) and sults indicate that, when a combination of BINAP xantphos (0.01 mmol) resulted in a slight decrease in and xantphos was used, each phosphane functions the reaction rate (TOF=10.9 hÀ1), although the uniquely and specifically (BINAP in the decarbonyla- linear-selectivity (2-l/2-b=94/6) remained the same. tion and xantphos in the hydroformylation), to ach- These findings suggest that, for the simultaneous use ieve the highly linear-selective hydroformylation, as of BINAP and xantphos, the rhodium species associ- we expected. ated with the xantphos ligand controls the regioselec- tivity and the efficiency of the overall reaction. Furthermore, 31P NMR experiments (Figure 1) im- plied that two rhodium species participate in the reac- Table 1. Effective use of a combination phosphanes in ACHTUNGRE Rh(I)-catalyzed hydroformylation of 1-decene 1 using for- tion of entry 1 in Table 1. A mixture of [RhCl(cod)]2, malin.[a] (R)-BINAP, and xantphos (1:2:2) in toluene-d8 at room temperature showed two signals at d=49.5 ppm (d, JP,Rh = 195 Hz) and 2.3 ppm (d, JP,Rh =91 Hz), [11] which correspond to [RhCl((R)-BINAP)]2 and RhCl(cod)ACHTUNGRE (xantphos),ACHTUNGRE [12] respectively. When 100 equivalents of formalin were added to the mixture, these signals vanished, and two new signals appeared at d=45.6 ppm (dd, JP, P =45 Hz, JP,Rh = 160 Hz) and 20.9 ppm (d, JP,Rh =127 Hz), which are assigned to [11b] RhCl(CO)((R)-BINAP) and RhH(CO)2 (xantphos),ACHTUNGRE [9] respectively. These two rhodium species, ACHTUNGRE RhCl(CO)((R)-BINAP) and RhH(CO)2(xantphos), would be directly involved in the linear-selective hy- droformylation catalysis using formaldehyde in the presence of both BINAP and xantphos. From the above results, an acceptable reaction pathway is as follows. Thus, the present reaction in- cludes two catalytic processes: the decarbonylation of Entry BINAP xantphos Conv.[b] Yield (2-l/2-b)[b] formaldehyde leading to the formation of a carbonyl moiety and H and subsequent hydroformylation 1 2 mol% 2 mol% 98% 80% (97/3) 2 2 4 mol% – 85% 85% (64/36) using the resulting carbonyl moiety and H2 3 – 4 mol% 77% 8% (88/12) (Scheme 1). Each process proceeds in a general manner. Oxidative addition of the aldehydic CÀH [a] Conditions: 1 (1 mmol), formalin (37%; 0.37 mL, bond in formaldehyde to Rh, followed by decarbony- ACHTUNGRE 5 mmol), [RhCl(cod)]2 (0.01 mmol), ligand (0.04 mmol), lative hydride migration and subsequent reductive 8 toluene (6 mL), 90 ,20h. elimination, yields an Rh-CO species and H . On the [b] Yields are the sum of 2-l and 2-b. Values in parentheses 2 are the ratios of 2-l/2-b. Conversions, yields, and ratios other hand, addition of in situ generated Rh-H species were determined by GC. cod= 1,5-cyclooctadiene; to 1-alkene and subsequent insertion of the carbonyl BINAP=2,2’-bis(diphenylphosphino)-1,1’-binaphthyl; formed earlier, followed by hydrogenolysis by H2, xantphos=9,9-dimethyl-4,5-bis(diphenylphosphino)xan- afford the aldehyde with the regeneration of the Rh- thene. H species. These are taken up by two different rhodi- 300 asc.wiley-vch.de 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Synth. Catal. 2010, 352, 299 – 304 Highly Linear-Selective Hydroformylation of 1-Alkenes using Formaldehyde 31 ACHTUNGRE Figure 1. P NMR spectra of (a) a mixture of [RhCl(cod)]2,(R)-BINAP, and xantphos (1:2:2) in toluene-d8 solution and (b) the reaction of the mixture with formalin.