Synthesis of 1‐Aza‐2‐borabutatriene Rhodium Complexes by Thermal Borylene Transfer from [(OC)₅MoBN(SiMe₃)₂]

Abstract

Since the first reports of allenes more than a century ago [1] compounds with cumulated double bonds have attracted interest owing to their highly unsaturated structure.[3]-Cumulene, or butatriene (I), consists of three cumulated carbon-carbon double bonds that can potentially ligate to a transition-metal center. However, they coordinate mostly in an h 2 -p fashion through the central C = C bond. [2] As reported by the groups of Hughes and Lentz, the highly reactive molecule tetrafluorobutatriene (which decomposes slowly even at À80 8C) can be trapped and stabilized by transitionmetal coordination (VII).[3] In 2002, Suzuki et al. reported the coordination of a butatriene to low-valent zirconocene in a novel k 2 -s,s bonding mode, the first example of a fivemembered metallacycloalkyne. [4] As boron-based p systems have attracted much attention owing to their interesting photophysical properties, [5] we turned our attention to boron-containing cumulene systems. Amino(methylene)boranes (V), isoelectronic to allenes (IV), can be isolated when the kinetically unstable B = C bond is sterically protected by bulky substituents. Structural characterization revealed that such amino(methylene)boranes adopt an allene-like structure with a linear N=B=C skeleton.[6] Furthermore, there are a few examples of boroncontaining ionic allene analogues such as the 1,3-borataallene dianion and the 2-borataallene anion.[7] The attempt to synthesize 1-boraallene (VI) by the reaction of an alkynylfluoroborane with tert-butyllithium at À120 8C afforded the corresponding boraallene only as an intermediate, which promptly underwent a hydroalkylation reaction at the B=C bond.[8]B-amino-1-boraallenes (II) are isoelectronic to butatriene (I) and might represent boron-containing [3]-cumulene systems when the boron-nitrogen p interaction is taken into account. Currently, very little is known about this class of compounds, and no successful synthetic approach has been reported. Ab initio calculations on the parent compound II and its constitutional isomer aminoborirene III have been carried out [9] suggesting that II is 12.9 kcal mol À1 higher in energy than III, which is surprising given the borirenes 2 pelectron aromatic stabilization.[10] Ever since a facile synthetic route to Group 6 terminal borylene complexes was developed, [11] they have proven excellent sources for the borylene fragment.[12] This borylene transfer method has developed quickly in the past decade and has been applied to the synthesis of borirenes, [13] new transition-metal borylene complexes, [12,14] metathesis reactions, [15] and the insertion of the DBÀR fragment into olefinic CÀH bonds.[16]One particularly intriguing and unexplored area of transition-metal borylene chemistry is their reactivity with (and perhaps transfer to) metal-carbon multiple bonds. Given this paucity and our motivation towards the synthesis of B-amino-1-boraallenes (II), we decided to investigate the behavior of terminal Group 6 metal borylenes with vinylidenerhodium complexes. Herein, we report ...

Boron‐ versus Nitrogen‐Centered Nucleophilic Reactivity of (Cyano)hydroboryl Anions: Synthesis of Cyano(hydro)organoboranes and 2‐Aza‐1,4‐diborabutatrienes

“…5 a/b R may thus be regarded as the first examples of 2‐aza‐1,4‐diborabutatrienes. Other reported azaborabutatrienes include a 1‐aza‐2‐borabutatriene rhodium complex generated by borylene transfer from a molybdenum aminoborylene complex to a rhodium vinylidene, [39] as well as a couple of aminoborylacetylenes Et 2 N−C≡C−BY 2 (Y=Mes, NMe 2 ),[ 40 , 41 ] which show significant contribution from their 1‐aza‐4‐borabutatriene resonance forms, Et 2 N=C=C=BY 2 .…”

Direkte Umwandlung eines terminalen Borylen‐ in einen terminalen Phosphinidenkomplex

“…[16] Dagegen ist der terminale Alkylborylenkomplex [(h 5 -C 5 H 5 )(OC) 2 Mn=BtBu] (1)z ur Aktivierung ungesättigter polarer Moleküle befähigt, was 1) Metathesen mit Ketonen unter Bildung von terminalen Alkylidenkomplexen, [17] 2) Lewis-Basen-induzierte intramolekulare Ligandkupplungen [18] oder 3) C-H-Aktivierungen ermçglichte. [19] Die hier vorgestellten Ergebnisse zeigen einen weiteren, bislang beispiellosen Reaktionspfad von 1 auf.Soführt die Umsetzung von 1 mit [ClPNMes*] (Mes* = 2,4,6-Tri-tert-butylphenyl) zu dem ersten stabilen terminalen Manganphosphinidenkomplex [(h 5 -C 5 H 5 )(OC) 2 Mn=PN-(Mes*)(BtBuCl)] (2;S chema 1). [20] Mithilfe experimenteller und theoretischer Methoden wurden dessen Struktur und Bindungssituation sowie der zugrundeliegende Reaktionsmechanismus detailliert untersucht.…”

Cobalt, rhodium and iridium

“…34 Addition of CpRh(PR 3 )QCQCH 2 32 (R = i Pr, Cy) to (CO) 5 MoQBQN(SiMe 3 ) 2 33 in C 6 H 6 and warming to 40 1C gave 34a and CpRh(CO)(P i Pr 3 ) in a 2 : 1 ratio. 35 This journal is © The Royal Society of Chemistry 2012…”