Chemistry of N,S‐Heterocyclic Carbene and Metallaboratrane Complexes: A New η³‐BCC‐Borataallyl Complex

Abstract

A high-yielding synthetic route for the preparation of group 9 metallaboratrane complexes [Cp*MBH(L)2], 1 and 2 (1, M=Rh, 2, M=Ir; L=C7H4NS2) has been developed using [{Cp*MCl2}2] as precursor. This method also permitted the synthesis of an Rh-N,S-heterocyclic carbene complex, [(Cp*Rh)(L2)(1-benzothiazol-2-ylidene)] (3; L=C7H4NS2) in good yield. The reaction of compound 3 with neutral borane reagents led to the isolation of a novel borataallyl complex [Cp*Rh(L)2B{CH2C(CO2Me)}] (4; L=C7H4NS2). Compound 4 features a rare η(3)-interaction between rhodium and the B-C-C unit of a vinylborane moiety. Furthermore, with the objective of generating metallaboratranes of other early and late transition metals through a transmetallation approach, reactions of rhoda- and irida-boratrane complexes with metal carbonyl compounds were carried out. Although the objective of isolating such complexes was not achieved, several interesting mixed-metal complexes [{Cp*Rh}{Re(CO)3}(C7H4NS2)3] (5), [Cp*Rh{Fe2(CO)6}(μ-CO)S] (6), and [Cp*RhBH(L)2W(CO)5] (7; L=C7H4NS2) have been isolated. All of the new compounds have been characterized in solution by mass spectrometry, IR spectroscopy, and (1)H, (11)B, and (13)C NMR spectroscopies, and the structural types of 4-7 have been unequivocally established by crystallographic analysis.

η4‐HBCC‐σ,π‐Borataallyl Complexes of Ruthenium Comprising an Agostic Interaction

“…[17] Borataallyl complexes are of particular significance because of their enhanced reactivity compared with the analogous cyclic p-ligands.T he h 3 -BCC-coordinated alkyl-boranesa re rare and the precedence are mostly restricted to platinum complexes of general formula [(R) n Pt{h 3 -BCC-VB Ph }], VI (when n = 1, R = tBu 3 P; n = 2, R = PPh 3 )a nd ar hodium complex [Cp*Rh-(C 7 H 4 NS 2 ) 2 B{CH 2 C(CO 2 Me)}], VIII. [16,19] Several bondingd escriptions of h 3 -and h 4 -coordinated vinylborane ligandswithatransition-metal centera re showni nF igure 2. [16,17,19,20] The presence of au nique Ru-H-B interaction in 2b compared with other reported h 3 -BCC-coordinated speciesr aise questionso n the nature of bonding in 2b.T he longer Ru1ÀH1 (1.72(3) ) and shorter B1ÀH1 (1.183(18))b ond distances in 2b hints at the presence of an agostic-type interaction, as in the case of the chromium(0) olefin complex [(OC) 4 Cr{(H 3 C) 3 CHC=CHBH-N(SiMe 3 ) 2 }], VII,l eading to as lightly elongated RuÀBb ond.…”

“…[16,19] Several bondingd escriptions of h 3 -and h 4 -coordinated vinylborane ligandswithatransition-metal centera re showni nF igure 2. [16,17,19,20] The presence of au nique Ru-H-B interaction in 2b compared with other reported h 3 -BCC-coordinated speciesr aise questionso n the nature of bonding in 2b.T he longer Ru1ÀH1 (1.72(3) ) and shorter B1ÀH1 (1.183(18))b ond distances in 2b hints at the presence of an agostic-type interaction, as in the case of the chromium(0) olefin complex [(OC) 4 Cr{(H 3 C) 3 CHC=CHBH-N(SiMe 3 ) 2 }], VII,l eading to as lightly elongated RuÀBb ond. [16b] The exo-positions of the coordinated vinyl group are occupied by the vinyl proton (H25B) and the B-2-mbzt ring (N2), which lie 0.631 and 1.128 a bove the B1-C26-C25 plane respectively.…”

“…[21] Some structural parameters of various h 3 -BCC-and h 4 -HBCC-coordinated metal complexesa re listed in Table S1 to authenticate the presence of h 4 -HBCC interaction in 2b. [16][17][18][19][20][21] To understand the bondingi nteraction between Ru and BCC unit of 2a-c,q uantum chemical calculations were carriedo ut at the B3LYP{SDD,6-31G(d,p)} level of theory. [22] The borane/ alkene and borataallyl complexes can be distinguishedb ym olecular orbitala nalysis of BÀCÀCm olecular orbitals involved in MÀ(BCC) bonding.…”

An Efficient Method for the Synthesis of Boratrane Complexes of Late Transition Metals

“…Thus, we anticipated that [(η 6 ‐ p ‐cymene)RuCl 2 ] 2 could be a potential precursor for the generation of p ‐cymene‐based ruthenaboratrane complexes. As a result, in an attempt to synthesize the Ru analogue of the rhodaboratrane complex [Cp*RhBH(L) 2 ] (L=C 7 H 4 NS 2 ),, we carried out reactions of [(η 6 ‐ p ‐cymene)RuCl 2 ] 2 with both [NaBt] (Bt=dihydrobis(2‐mercaptobenzothiazolyl)borate) and [NaBo] (Bo=dihydrobis(2‐mercaptobenzoxazolyl)borate). Unfortunately, all of our attempts to generate ruthenaboratrane complexes were unsuccessful.…”

“…In an effort to find efficient methods for the preparation of such complexes, we used different synthetic precursors. One of the useful precursors identified was [Cp*MCl 2 ] 2 (M=Rh or Ir), which enabled us to isolate several metallaboratrane complexes in good yields ,. As a result, in an extension of our previous work, we explored this chemistry with Group 8 metals.…”