Incorporation of Boron into Uranium Metallacycles: Synthesis, Structure, and Reactivity of Boron‐Containing Uranacycles Derived from Bis(alkynyl)boranes

Abstract

The reaction of uranacyclopropene complex (C5Me5)2U[η2‐1,2‐C2(SiMe3)2] with B‐aryl bis(alkynyl)borane PhB(C≡CPh)2 led to the first six‐membered uranium metallaboracycle, while the reaction with B‐amino bis(alkynyl)borane (Me3Si)2NB(C≡CPh)2 afforded an unexpected uranaborabicyclo[2.2.0] complex via [2+2] cycloaddition. The reaction with CuCl revealed the non‐innocent property of the rearranged bis(alkynyl)boron species towards oxidant. The reactions with isocyanide DippNC: (Dipp=2,6‐iPr2‐C6H3) and isocyanate tBuNCO afforded the novel uranaborabicyclo[3.2.0] complexes. All new complexes have been structurally characterized. DFT calculations were performed to provide more insights into the electronic structures and the reaction mechanism.

Update for Reactions of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes: A Never-Ending Story?

“…In a series of publications, it was shown that it is possible to transfer the typical alkyne substitution reactivity of group 4 metallocene bis­(trimethylsilyl)­acetylene complexes to actinide metallacycles as well. , For this several papers from Zi, Walter, et al as well as from Kiplinger and co-workers , about synthesis and reactions of actinide metallocene bis­(trimethylsilyl)­acetylene complexes Cp′ 2 M­(η 2 -Me 3 SiC 2 SiMe 3 ) were published.…”

“…This was reported for different symmetrically and nonsymmetrically substituted alkynes to yield a wide variety of well-known metallacycles (metallacyclopentadienes, metallacyclocumulenes/metallacyclopentatrienes, metallacyclopentenes). Reactions with 9,10-phenanthrenechinone gave a monomeric uranium quinonate, whereas o -benzochinone furnished a dimeric quinonate . Very recently the synthesis, structure, and reactivity of well-defined scandacyclopropenes were described as well .…”

“…Very recently the synthesis, structure, and reactivity of well-defined scandacyclopropenes were described as well . As a modification to a literature procedure, again by reduction of the corresponding dichloride Cp* 2 UCl 2 with KC 8 in the presence of bis­(trimethylsilyl)­acetylene, Me 3 SiCCSiMe 3 , the complex Cp* 2 U­(η 2 -Me 3 SiC 2 SiMe 3 ) was obtained in a yield of 74% . The complex Cp* 2 U­(η 2 -Ph 2 PC 2 PPh 2 ) was synthesized, not via the substitution of bis­(trimethylsilyl)­acetylene, Me 3 SiCCSiMe 3 , by 1,2-bis­(diphenylphosphino)­acetylene, Ph 2 PCCPPh 2 , from the uranium metallocene complex Cp* 2 U­(η 2 -Me 3 SiC 2 SiMe 3 ) with Ph 2 PCCPPh 2 but only by reducing the corresponding dichloride Cp* 2 UCl 2 with KC 8 in the presence of Ph 2 PCCPPh 2 .…”

Facile Synthesis of Uranium Complexes with a Pendant Borane Lewis Acid and 1,2‐Insertion of CO into a U−N Bond

“…Gratifyingly, the reaction of I with Ph 2 BCl yielded 3 , which was in full agreement with our hypothesis. In solution, complex 3 showed a broad resonance at δ B 83.9, which is comparable to that of Ph 2 BMe ( δ B 70.6) [15] and an isolable uranium metallaboracycle ( δ B 76.0) [16] . The single crystal structure of 3 revealed a dangling trigonal planar Ph 2 B(alkyl) moiety as indicated by the sum of angles (360.0°) around the boron center.…”

“…In solution, complex 3 showed a broad resonance at δ B 83.9, which is comparable to that of Ph 2 BMe (δ B 70.6) [15] and an isolable uranium metallaboracycle (δ B 76.0). [16] The single crystal structure of 3 revealed a dangling trigonal planar Ph 2 B(alkyl) moiety as indicated by the sum of angles (360.0°) around the boron center. The trigonal bipyramidal geometry around the uranium nucleus in 3 resembles its precursor I.…”