Activation of boryl-, borylene and metalloborylene complexes by isonitriles

Abstract

The reactions of isonitriles with a variety of metalloboryl and metalloborylene species are shown to yield a range of products, none of which display the typical Lewis acid-base reactivity previously observed between such metal complexes and other Lewis bases. Insertions of one, or several, isonitriles into the metal-boron bond give cyclic and spiro compounds with bonding controlled by the electron count at the metal and in the ring.

Interactions of Isonitriles with Metal–Boron Bonds: Insertions, Coupling, Ring Formation, and Liberation of Monovalent Boron

“…The 1 H NMR spectrum of 12 shows three t Bu proton signals in a 18:9:9 ratio, which suggests multiple additions of isocyanide to the complex. The 11 B NMR spectrum of 12 shows a resonance at δ =−6.6 ppm, which is nearly identical to that of the previously published iron boryl monoinsertion product 14 d ( δ =−6.3 ppm; Scheme ) . The crystallographically derived structure of the complex 12 (Figure ) confirmed the multiple insertion of isonitrile units suggested by the 1 H NMR data.…”

“…Recently, we reported the reaction of an iron boryl complex with tert ‐butylisonitrile, which led to the full insertion of the isonitrile into the Fe−B bond and the formation of a three‐membered BCN ring (complex 14 d , see Scheme ), similar to those seen in complexes 5 b – 8 b . Inspired by this reaction, the Mn I boryl complex [(Cy 3 P)(OC) 4 Mn(BCl 2 )] ( 11 ) was treated with differing amounts of tert ‐butylisonitrile at room temperature.…”

“…The construction of complex 4 is even more surprising considering that complex 2 (a carbene‐stabilized derivative of 1 ), when treated with one equivalent of the same isocyanide (CN t Bu), was previously shown to undergo full isocyanide insertion into the M−B bond leading to the formation of a three‐membered ring and a metal−carbon double bond in the complex 5 b (Scheme ) . In this reaction, no evidence for a complex analogous to 4 (i.e., isomer 5 a in Scheme ) was observed, which would merely be the partially isonitrile‐inserted isomer of 5 b .…”

“…However, it is only very recently that the reactions of boryl and borylene complexes with isonitriles have been substantially addressed . This work has already uncovered a number of unusual reactivity patterns, such as single isonitrile insertion and three‐membered ring formation from boryl and base‐stabilized borylene complexes, as well as the double insertion of isonitriles into M=B double bonds and their C−C coupling leading to four‐membered heterocyclic carbene complexes (see Scheme ) ,. Very recently, the addition of isonitriles to borylene complexes also led to both interrupted and complete liberation of the borylene ligand as formally monovalent boron species, including the base‐stabilized borylene monocarbonyl [TpB(=C=O)(CNDipp)] (Tp=2,6‐bis(2,4,6‐triisopropylphenyl)phenyl, Dipp=2,6‐diisopropylphenyl) and bis‐isonitrile species of the form [ArB(CNR) 2 ] (Ar=Tp, R=Me; Ar=Dur=2,3,5,6‐tetramethylphenyl, R=Dipp) …”

Striking transformations of the hydroborylene ligand in a HB:→NiIIcomplex with isocyanides and CO

“… 12 More recently, we reported on the first example of a terminally coordinated :BH ligand, in the hydroborylene Ni II complex [{cat( TMS L)Si}(Cl)Ni←:BH (NHC) 2 ], 1 (cat = ortho -C 6 H 4 O 2 ; TMS L = N(SiMe 3 )(Dipp); Dipp = 2,6-Pr i 2 C 6 H 3 ; NHC = :C[(Pr i )NC(Me)] 2 ). 13 Related terminal borylene-TM complexes have been shown to undergo diverse and remarkable reactivity towards isocyanides and carbon monoxide, 11 , 14 , 15 including the multiple coordination of CO at a B I centre ( Fig. 1 ).…”