Stable Two‐Legged Parent Piano‐Stool and Mixed Diborabenzene‐E₄ (E=P, As) Sandwich Complexes of Group 8

Abstract

A cyclic alkyl(amino)carbene-stabilized 1,4diborabenzene (DBB) ligand enables the isolation of 18electron two-legged parent piano-stool Fe 0 and Ru 0 complexes, [(η 6 -DBB)M(CO) 2 ], the ruthenium complex being the first of its kind to be structurally characterized.[(η 6 -DBB)Fe(CO) 2 ] reacts with E 4 (E = P, As) to yield mixed DBB-cyclo-E 4 sandwich complexes with planar E 4 2À ligands. Computational analyses confirm the strong electron-donating capacity of the DBB ligand and show that the E 4 ligand is bound by four equivalent FeÀ P σ bonds.

Synthesis and Reactivity of Highly Electron-Rich Zerovalent Group 10 Diborabenzene Pogo-Stick Complexes

“…It is noteworthy that the M···DBB centroid distance in 3-M is only slightly shorter than that in the structurally related palladium­(II) and platinum­(II) 9,10-diborataanthracene complexes, [(η 6 -C 12 H 8 B 2 Me 2 )­M­(cot)] (M = Pd 1.87, Pt 1.85 Å; cot = cyclooctatetraene) . In both 3-Pd and 3-Pt , the CAAC ligands adopt an anti conformation relative to each other, similar to the related group 8 complexes VI-M , and the C 4 B 2 rings are slightly distorted out of planarity (endocyclic torsion angles for 3-Pd 2.2(7)–5.9(8)°; 3-Pt 2.1(4)–7.3(5)°). Furthermore, bonding to the DBB ring is relatively unsymmetrical (Pd–B 2.417(5), 2.439(5) Å; Pd–C DBB 2.360(4)–2.421(4) Å; Pt–B 2.424(3), 2.428(3) Å; Pt–C DBB 2.326(3)–2.426(3) Å).…”

“…The replacement of endocyclic carbon units with isosteric and isoelectronic boron fragments within aromatic compounds has been shown to deeply affect the energies of the frontier molecular orbitals (MOs) and thus the electronic properties and reactivity of the resulting boracarbocycles. − 1,4-Diborabenzene (DBB) and the related 9,10-diboraanthracence derivatives, in particular, have started to show great potential for the activation of small molecules between their two boron centers − and as highly electron-donating 6π-aromatic ligands for the stabilization of half-sandwich complexes. − Thus, the doubly cyclic alkyl­(amino)­carbene (CAAC)-stabilized 1,4-diborabenzene 1 (see Figure ) has been used to stabilize three- and two-legged parent half-sandwich complexes of groups 6 ( V-M ) and 8 ( VI-M ), respectively, , as well as the first examples of stable actinide arene half-sandwich complexes …”

“…36−41 1,4-Diborabenzene (DBB) and the related 9,10-diboraanthracence derivatives, in particular, have started to show great potential for the activation of small molecules between their two boron centers 41−43 and as highly electron-donating 6π-aromatic ligands for the stabilization of half-sandwich complexes. 44−46 Thus, the doubly cyclic alkyl(amino)carbene (CAAC)stabilized 1,4-diborabenzene 1 (see Figure 2) 47 has been used to stabilize three-and two-legged parent half-sandwich complexes of groups 6 (V-M) and 8 (VI-M), respectively, 44,45 as well as the first examples of stable actinide arene halfsandwich complexes. 46 In this contribution, we report the synthesis, spectroscopic and structural characterization, electronic properties, and preliminary reactivity of zerovalent nickel, palladium, and platinum diborabenzene complexes of the form [(η 6 -DBB)-M 0 L] (M = Ni, L = CO; M = Pd, Pt, L = norbornene = nbe), of which the platinum complex is the first example of an isolated Pt(0) arene complex.…”

CAAC-stabilised 9,10-diboraanthracene: an electronically and structurally flexible platform for small-molecule activation and metal complexation

“…Given the strong electron-donating properties of the related doubly CAAC-stabilised 1,4-diborabenzene (DBB), which has been exploited by our group for the synthesis of unusual halfsandwich complexes of low-valent group 6, 8 and 10 metals, as well as actinides, [25][26][27][28] we decided to explore the use of DBA II as a ligand in transition metal chemistry. The reaction of DBA II with [(MeCN) 3 M(CO) 3 ] (M = Cr, Mo, W) cleanly afforded the three-legged half-sandwich complexes [(η 6 -DBA)M(CO) 3 ] (4-M) (M = Cr, Mo, W) after 4 days at 60 °C, accompanied by a colour change to dark green.…”

Redox Chemistry of an End-Deck cyclo-As3 Nickel Complex

“…Tremendous attention has been paid to polyphosphorus ligand complexes, mainly in the context of (transition) metal-mediated activation and conversion of white phosphorus (P 4 ). − In contrast, representatives of E n complexes of the heavier homologs As, Sb, and Bi are far less known, which is commonly attributed to the lower homoatomic E – E bond energies . Nevertheless, especially As n complexes raised considerable interest from very early on, as indeed the first reported E n ligand complexes contain an As 2 and a cyclo -As 3 ligand, respectively. , Since then, cyclo -As n ligand complexes bearing cyclo -As 3 , ,− cyclo -As 4 , − cyclo -As 5 , − cyclo -As 6 and even cyclo -As 8 ligands, which are related to the respective hydrocarbons via the isolobal principle, have been isolated, often using yellow arsenic (As 4 ) . Other representatives include transition metal polyarsenides, such as the recently isolated binary Fe/As Zintl cluster [Fe 3 (As 3 ) 3 As 4 ] 3– or organometallic polyarsenides, as e.g., [{Cp*Co} 3 (μ 3 ,η 4:4:4 -As 6 )] 0/+/2+ (Cp* = C 5 Me 5 ). , One field of particular interest is the redox chemistry of such E n ligand complexes, as, on the one hand, it allows to study the redox properties of these species which are otherwise inaccessible and, on the other hand, grants access to completely unprecedented E n structural motifs.…”