Synthesis and Crystal Structures of P-Iron-Substituted Phosphinoborane Monomers

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• 作者：Kazuyuki Kubo ; Tomohiro Kawanaka ; Masao Tomioka ; Tsutomu Mizuta
• 刊名：Organometallics
• 出版年：2012
• 出版时间：March 12, 2012
• 年：2012
• 卷：31
• 期：5
• 页码：2026-2034
• 全文大小：535K
• 年卷期：v.31,no.5(March 12, 2012)
• ISSN：1520-6041

文摘

A family of P-iron-substituted phosphinoboranes, Cp(CO)₂Fe{P(Ar)BMes₂} (Ar = Ph, Mes, Tipp, Mes*), have been prepared from the reaction of Cp(CO)₂FeCl and (Li)(Ar)PBMes₂. All the complexes have been characterized successfully by ¹H, ¹¹B, and ³¹P NMR; IR spectroscopy; and X-ray crystallography. In the IR spectra, all the complexes display similar carbonyl stretching frequencies that are remarkably higher than those of closely related phosphide complexes. These observations indicate that a repulsive interaction between the filled d orbital on the iron and the lone pair on the phosphorus is less severe in the studied iron-phosphinoboranes, which is most likely because of the P鈫払 蟺 interaction that occurs in them. The ³¹P{¹H} NMR chemical shifts of the phosphinoborane phosphorus move upfield with the increasing steric bulk of the Ar groups in the order Ph (鈭?1.4 ppm) < Mes (鈭?8.8 ppm) < Tipp (鈭?4.9 ppm). However, the phosphorus bearing the most sterically demanding Mes* group appears at an unexpectedly downfield value of 鈭?4.9 ppm, which is probably reflective of its structural peculiarities. The ¹H NMR spectrum of each complex displays two sets of signals, assignable to inequivalent Mes groups on the boron atom, as a consequence of a hindered rotation around the P鈥揃 bond. This high rotational barrier most likely results from the significant double-bond character in the P鈥揃 bond. The X-ray diffraction studies have confirmed the iron-phosphinoboranes considered herein to be monomeric species. Each molecule consists of a nearly planar phosphinoborane fragment with a short P鈥揃 bond. The Fe鈥揚 bond is notably elongated as the Ar group becomes larger, demonstrating its somewhat vulnerable nature with respect to steric congestion. In contrast, the variation in the P鈥揃 bond distance is relatively small throughout the series of iron-phosphinoboranes, suggesting that the P鈺怋 double-bond character is balanced by steric and electronic effects of the substituents around the phosphorus.