Reductive Borylene–CO Coupling with a Bulky Arylborylene Complex

Abstract

Partial metal-boron bond cleavage and coupling of a borylene with two CO ligands was observed upon reduction of a new bulky arylborylene complex. Both the borylene precursor and dianionic product were structurally and spectroscopically characterized. In contrast, reduction of an aminoborylene complex led to complete loss of the borylene ligand and classical Hieber reduction. A rationale for these differences based on DFT methods is presented.

Release of Isonitrile‐ and NHC‐Stabilized Borylenes from Group VI Terminal Borylene Complexes

“…Extremely broad 11 B NMR signals are observed for complexes 2 a – f , which fall in the range of 145–155 ppm, as has been previously reported in similar terminal arylborylene complexes . Compounds 2 b , 2 d and 2 e have been characterized by X‐ray crystallographic studies (Figure ), whereas the molecular structures of 2 a and 2 c were published in our original reports . The metal–boron distances for the Cr borylenes are identical within experimental error, ranging from 1.913(2) Å in 2 a to 1.904(5) Å in 2 c , whereas the M−B distances of the W borylenes are 2.069(12) and 2.079(4) Å in 2 d and 2 e , which are within the ranges reported for terminal borylene M−B distances ,.…”

“…Solid‐state IR spectroscopy reveals A 1 symmetric carbonyl vibrational modes between 2063–2067 cm −1 for 2 a – 2 c and 2073–2078 cm −1 for 2 d – 2 f , which is indicative of the relative electron deficiency of the metal center in relation to known σ‐donor complexes ([(1,3‐dimethylimidazol‐2‐ylidene)Cr(CO) 5 ] has an A 1 symmetric stretching frequency of 2056 cm −1 ) . This observation is in line with the significant π‐backdonation from the metal center to the unsaturated arylborylene moiety …”

“…Compounds 2 b , 2 d and 2 e have been characterized by X‐ray crystallographic studies (Figure ), whereas the molecular structures of 2 a and 2 c were published in our original reports . The metal–boron distances for the Cr borylenes are identical within experimental error, ranging from 1.913(2) Å in 2 a to 1.904(5) Å in 2 c , whereas the M−B distances of the W borylenes are 2.069(12) and 2.079(4) Å in 2 d and 2 e , which are within the ranges reported for terminal borylene M−B distances ,. Solid‐state IR spectroscopy reveals A 1 symmetric carbonyl vibrational modes between 2063–2067 cm −1 for 2 a – 2 c and 2073–2078 cm −1 for 2 d – 2 f , which is indicative of the relative electron deficiency of the metal center in relation to known σ‐donor complexes ([(1,3‐dimethylimidazol‐2‐ylidene)Cr(CO) 5 ] has an A 1 symmetric stretching frequency of 2056 cm −1 ) .…”

Reaktivität eines Dihydrodiborens gegen CO: Koordination, Insertion, Spaltung und spontane Bildung eines cyclischen Alkins

“…Using first-row transition metal borylene precursors, we have reported several examples of base-triggered borylene-carbonyl coupling reactions, [19] the reductive coupling of a borylene to two CO ligands at chromium, [20] as well as the complete cleavage of CO at an iron(0) bis(borylene) complex upon coordination of a cAAC ligand. [21] Addition of strong σ-donor π-acceptor ligands (cAAC, CO, RNC) to iron and manganese borylene carbonyls provided facile routes to tricoordinate CO-stabilized metal-free borylenes.…”

Synthese und Nachweis von Iminoboranen durch M=B/C=N‐Bindungsmetathese

“…Unsere jüngsten Synthesen von neutralen terminalen Arylborylenkomplexe der Form [(Me 3 P)(OC) 3 M(BAr)] (M = Fe,R u) und [(OC) 5 M(BAr)] (M = Cr,M o) [10] hat zur Entdeckung von einer Vielzahl an neuen Reaktivitätsprofilen geführt, welche fürd ie konventionellen Aminoborylen-und kationischen Arylborylenkomplexe unbekannt sind. [2] Diese neutralen terminalen Borylenkomplexe weisen im Allgemeinen eine hohe Reaktivitäta uf und zeigen eine ausgeprägte Neigung zur vollständigen M = B-Bindungsspaltung, was sich in der Freisetzung des Borylenfragments und der Bildung monovalenter Borspezies in Gegenwart von verschiedenen Donoren wie Isocyaniden oder CO widerspiegelt.…”