Diboran(4)yl Groups as Ligands to Transition Metals

Abstract

Recently, several transition metal boryl compounds were characterized, most of them containing the 1,2-phenylenedioxy group (1,2-02C6H4 = cat) as ligand to boron[". In general, these compounds had been obtained by oxidative addition of (cat)BH to complexes of late transition metals or by salt elimination from (cat)BCl and anionic transition metal complexes. Corresponding reactions with diborane(4) derivatives proceed with cleavage of the boron-boron bond and addition of the boron-containing fragments to the metal center, again yielding boryl complexes [*]. In the case of the reaction of several 1,2-dichlorodiboranes with K[(q5-C5H4Me)Mn(SiMePh2)(CO)2] a different reaction was found. The diboranes reacted with formation of binuclear manganese complexes with a bridging borylene group BR (R = NMe2, tBu), and (RBH2)* was found as boron-containing byproduct [']. In this paper we report on the syntheses and structures of the first transition metal-substituted diborane(4) compounds. Results and Discussionwith B2(NMe2j2C12 yields the transition metal diboranyl complexes la, b according to Eq. (1).These compounds were isolated as brown or dark yellow crystals, which can be handled in air for short periods and can be stored under nitrogen at room temperature. In solution both complexes la, b show two charactcristic I'B-NMR shifts 6 = 39.0 and 69.5 and 6 = 40.3 and 62.7, respectively. The signals at higher field are in the same region as the shift of the starting material at 8 = 37.5r41, the signals of the transition metal-substituted boron atoms, however, exhibit the expected low-field shift of 20-30 ppm. The four methyl groups of both compounds bound to nitrogen show four signals in the 'H-and ',C-NMR spectra, respectively, which is due to a restricted rotation with respect to the B-N bond.The X-ray structure analyses reveal that both molecules adopt a C1 symmetry in the crystal. The boron and nitrogen atoms are trigonal-planar-coordinated and both boryl groups are almost perpendicular to each other (dihedral angle for la, b: 92.4 and 92.3", resp.). The B-N distances are in a range of 137.6(3) and 138(1) pm and the B-B distances amount to 168.3(3) and 169(1) pm, respectively. Hence, the geometry of la, b is comparable to other structurally characterized diborane(4) derivatives having two dimethylaminoThe metal boron distances are 209.0(3) and 237.0(8) pm, respectively, thus being 13 and 18 pm longer as for known boryl complexes of iron and tungsten ['].The substitution of one chloro ligand by the [M(Cp)(CO),] group according to Eq. (I) proceeds under mild conditions in good yields. Exchange of the second chlorine, however, fails even in refluxing toluene, obviously for steric reasons.The described compounds are the first examples for diboran(4)yl groups as boron-bound ligands to transition metals. The absence of the catechol group as shbilizing ligand for such boryl complexes opens up the perspectives of investigating the reaction behaviour of metal-coordinated boron which is yet unknown. Possible reactions which are wort...

Aminoborylene Complexes of Group 6 Elements and Iron: A Synthetic, Structural, and Quantum Chemical Study

“…[24] Compounds of this type are also the thermodynamic products of the reactions involving 1,2-B 2 A C H T U N G T R E N N U N G (NMe 2 ) 2 I 2 , with the boryloxycarbyne complexes undergoing a thermal rearrangement to the mixed boryloxycar-…”

Kombination aus Boryl‐ und dativer Pt‐B‐Bindung: ein unerwarteter Koordinationsmodus für den Diboran(4)yl‐Liganden

“…Der letztere Prozess läuft für eine Reihe verschieden substituierter Halogenborane XBR 2 glatt ab und wurde daher ausgiebig zur Synthese von Borylkomplexen genutzt. [2] Dagegen sind entsprechende Reaktivitätsstudien an halogenierten Diboranen(4) immer noch selten, was im Hinblick auf die große Bedeutung von Diboranen (4) 2 Pt(Cl){B(NMe 2 )(Cl)}] weisen auf eine selektive Aktivierung der B-B-Bindung hin. [3] Ein alternativer Zugang zu Übergangsmetall-Diboran(4)ylKomplexen wurde von unserer Gruppe entwickelt: Wir zeigten, dass die Diboran(4)yl-Einheit glatt über Salzeliminierungsreaktionen von B 2 (NMe 2 )X 2 (X = Cl, [4] Br, [5] I [6] ) mit anionischen Halbsandwich-Carbonyl-Spezies M'[CpM(CO) n ] (M' = Na, K; M = Mo, W, Fe, Ru) eingeführt werden kann.…”

“…In diesem Fall gab es jedoch keine Hinweise auf eine oxidative Addition der B-Cl-Bindung, und die erhaltenen Produkte cis-[(Ph 3 P) 2 Pt-{B(NMe 2 )(Cl)} 2 ] und trans-[(Ph 3 P) 2 Pt(Cl){B(NMe 2 )(Cl)}] weisen auf eine selektive Aktivierung der B-B-Bindung hin. [3] Ein alternativer Zugang zu Übergangsmetall-Diboran(4)ylKomplexen wurde von unserer Gruppe entwickelt: Wir zeigten, dass die Diboran(4)yl-Einheit glatt über Salzeliminierungsreaktionen von B 2 (NMe 2 )X 2 (X = Cl, [4] Br, [5] I [6] ) mit anionischen Halbsandwich-Carbonyl-Spezies M'[CpM(CO) n ] (M' = Na, K; M = Mo, W, Fe, Ru) eingeführt werden kann.Aufgrund unseres anhaltenden Interesses an der Über-gangsmetall-Bor-Chemie haben wir vor kurzem die Reaktivität von halogenierten Diboranen (4) (1) und trans-[(iPr 3 P) 2 Pt(Br){B(NMe 2 )B(NMe 2 )(Br)}] (2) durch oxidative Addition einer B-Br-Bindung an die jeweiligen Platinvorstufen zu erhalten. …”

Phosphine-Substituted Diborane(4)yl Complexes of Tungsten

“…Reaction of 1,2-diaminodihalodiboranes(4) with anionic transition metal complexes has led to the first diborane(4)yl complexes [(η 5 -C 5 H 5 )(OC) n M-{B(NMe 2 )-B(NMe 2 )Cl}] [M(CO) n = Fe(CO) 2 ; M(CO) n = W(CO) 3 [4,5]], and [(η 5 -C 5 H 5 )(OC) n M-{B(NMe 2 )-B(NMe 2 )Br}] [M(CO) n = Ru(CO) 2 ; M(CO) n = Mo(CO) 3 (1) [4,6]] which were obtained via salt elimination reactions. The latter complex (1) was modified by PEt 3 /CO exchange to give the only phosphine-substituted diborane(4)yl complex [(η 5 -C 5 H 5 )(Et 3 P)(OC) 2 Mo-{B(NMe 2 )-B(NMe 2 )Br}] (2) [4,6] (eq.…”