Facile Carbon Monoxide Reduction at Intramolecular Frustrated Phosphane/Borane Lewis Pair Templates
Facile Carbon Monoxide Reduction at Intramolecular Frustrated Phosphane/Borane Lewis Pair Templates
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DOI：
10.1002/anie.201208750
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发表时间：
2013-01-01
影响因子：
16.6
通讯作者：
Erker, Gerhard
中科院分区：
文献类型：
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作者：
Sajid, Muhammad;Elmer, Lisa-Maria;Erker, Gerhard
寻找新的碳氧化物还原途径对于不断寻找碳氢化合物原料的新系统条目很重要。用容易获得的氢化物将CO转化为甲酰基是沿着这条道路迈出的重要一步。使用硼烷作为还原剂是可取的，也是潜在的有用的。合成了三烷基硼烷与一氧化碳的反应。HC Brown已经证明，R3B体系在100~1258℃的常压下很容易与CO反应，在氧化工作后生成各自的叔醇。[1]他们改进了这一过程，实现了酮和醛的合成。在后一种情况下，加入了锂铝氢化物试剂。[1，2]然而，一氧化碳出人意料地不愿与[B]H硼烷还原。据报道，一氧化碳在1008℃和20大气压下与B2H6反应生成“硼烷羰基”[H3B-CO]，这是一种在常压下分解的气体(BP±648C)。[5，6]我们现在发现，在受挫的磷烷/硼烷刘易斯对(FLP)[7，8]模板下，可以用合适的硼烷进行一氧化碳的还原。我们将体积较大的环戊烯基膦与氢化试剂[HB(C6F5)2][9]的混合物在RT下搅拌约15分钟，然后将得到的混合物置于一氧化碳气氛中(2bar)。反应12h后，还原产物2最终以63%的产率得到无色固体(见方案1)。以二氯甲烷/正戊烷为原料，合成了单晶2。在晶体化合物2中包含“η2-甲酰基”B(C6F5)2亚单位，该亚单位通过酰碳原子(C1)键合到磷原子，并通过酰基氧原子(O1)键合到FLP框架的硼中心(B1)(见图1和表1)。由此得到的六元杂环具有半椅状构象。环状B，C，O杂环丙烷亚基具有典型的元素-元素单键长度。碳(C_1)和硼(B_2)原子均呈准四面体配位构型，而铀型氧原子则呈扭曲的三角平面配位(键角之和为O_1：359.718)。X-射线晶体结构分析表明，得到了全反式非对映异构体2。
Finding novel pathways for the reduction of carbon oxides is important for the ongoing search for new systematic entries to hydrocarbon feedstocks. The CO to formyl conversion with readily available hydrides represents an important step along this way. Using boranes as the reducing reagents is desirable and potentially useful. Reactions of trialkylboranes with carbon monoxide are synthetically established. HC Brown had shown that R3B systems readily react with CO at 100 to 1258C at normal pressure to yield the respective tertiary alcohols after oxidative workup.[1] They modified this procedure to achieve the synthesis of ketones and aldehydes. In the latter case lithium aluminium hydride reagents were added.[1, 2] However, carbon monoxide is surprisingly reluctant to be reduced with [B] H boranes.[3, 4] Carbon monoxide is reported to react with B2H6 at 1008C and 20 atm to give “borane carbonyl”[H3B-CO], a gas (bp À648C) that dissociates at atmospheric pressure.[5, 6] We have now found that BÀH borane reduction of carbon monoxide can be carried out with a suitable borane at a frustrated phosphane/borane Lewis pair (FLP)[7, 8] template. We stirred a mixture of the bulky cyclopentenylphosphane 1 with the hydroboration reagent [HB (C6F5) 2][9] for about 15 minutes at RT and then subjected the resulting mixture to an atmosphere of carbon monoxide (2 bar). Workup after 12h at RT eventually gave the reduction product 2 as a colorless solid in 63% yield (see Scheme 1). Single crystals of 2 were obtained from dichloromethane/n-pentane. In the crystal compound 2 contains a “η2-formyl” B (C6F5) 2 subunit that is bonded through the acyl carbon atom (C1) to the phosphorus atom and through the acyl oxygen atom (O1) to the boron center (B1) of the FLP framework (see Figure 1 and Table 1). The resulting six-membered heterocycle features a half-chair-like conformation. The annulated B, C, O heterocyclopropane subunit features typical element–element single bond lengths. Both the carbon (C1) and the boron (B2) atoms show pseudo-tetrahedral coordination geometries, whereas the onium-type oxygen atom exhibits a distorted trigonal planar coordination pattern (sum of bond angles at O1: 359.718) The X-ray crystal structure analysis has revealed that the all-trans-diastereoisomer of 2 was obtained.