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

Abstract

In den letzten 15 Jahren haben Diborane(4) zunehmend an Bedeutung als wertvolle Reagentien in der katalytischen Funktionalisierung ungesättigter organischer Substrate gewonnen.[1] Die hier im Allgemeinen beobachtete Reaktivität der Diborane gegenüber der katalytisch aktiven Spezies, üb-licherweise niedervalente Metallkomplexe, beruht auf der oxidativen Addition der B-B-Bindung unter Bildung einer cis-Bis(boryl)spezies.[1] Beispielsweise ist die oxidative Addition von Tetraalkoxydiboranen (4) . 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.

Evidence for a Strong trans Influence of the Diboran(4)yl Ligand

“…[PtA C H T U N G T R E N N U N G (PiPr 3 ) 3 ], [14] trans-[(iPr 3 P) 2 Pt(Br){BA C H T U N G T R E N N U N G (NMe 2 )BA C H T U N G T R E N N U N G (NMe 2 ) 2 (Br)}] (5), [12] B 2 A C H T U N G T R E N N U N G (NMe 2 ) 2 I 2 , [13] and NaA C H T U N G T R E N N U N G [BAr F 4 ] [21] were prepared according to published procedures. NMR spectra were acquired either on a Bruker Avance 500 ( 1 H: 500.…”

“…(i) species obtained by a salt-elimination reaction of B 2 (NMe 2 ) 2 X 2 (X = Cl, [9] Br, [10] I [11] ) with anionic halfsandwich carbonyl . [12] A C H T U N G T R E N N U N G (iii) trans-[(iPr 3 P) 2 Pt(Br){BA C H T U N G T R E N N U N G (NMe 2 )BA C H T U N G T R E N N U N G (NMe 2 )(Br)}] (5) [12] For a more accurate description of the trans influence of the diboran(4)yl group, we set out to prepare the corresponding iodine derivative trans-[(iPr 3 P) 2 . We will also show that the diboran(4)yl ligands in 5 and 6 feature strong trans-labilizing abilities enabling selective halide abstraction reactions to afford T-shaped diboran(4)yl species trans-[(iPr 3 P) 2 Pt{BA C H T U N G T R E N N U N G (NMe 2 )BA C H T U N G T R E N N U N G (NMe 2 ) 2 (X)}]A C H T U N G T R E N N U N G [BAr F 4 ] (X= Br (7), I (8); Ar F = 3,5-(CF 3 ) 2 C 6 H 3 ).…”

“…As expected, the 31 P NMR spectrum of 6 shows a single 31 P NMR resonance with a chemical shift (d = 30.5 ppm) and a 1 JA C H T U N G T R E N N U N G (P,Pt) coupling constant (3106 Hz) highly characteristic for a trans-bisphosphine-Pt II species (compare with 5: d = 34.1 ppm; 1 JA C H T U N G T R E N N U N G (P,Pt) = 3118 Hz). [12] Accordingly, the 31 P NMR signal is shifted to higher field by 43 ppm with respect to that of [PtA C H T U N G T R E N N U N G (PiPr 3 ) 3 ] (d = 73.3 ppm; 1 JA C H T U N G T R E N N U N G (P,Pt) = 4101 Hz) [14a] upon changing the oxidation state of Pt and the 1 JA C H T U N G T R E N N U N G (P,Pt) coupling constant decreases at the same time.…”

“…The molecular structure of 6 rather resembles that of the bromine analogue 5, and the B1 À B2 (6: 1.738(6) ; 5: 1.742 (8) ), Pt1 À B1 (6: 2.087(4) ; 5: 2.073(5) ), Pt1 À B2 (6: 3.227 ; 5: 3.298 ) and PtÀP bond lengths (6: 2.3565(10) , 2.3241(10) ; 5: 2.3452(11) , 2.3146(11) ) are of similar magnitude. [12] However, the coordination of one boron center to platinum results in an elongation of the B1 À B2 bond by approximately 5 pm with respect to the diborane(4) precursor B 2 A C H T U N G T R E N N U N G (NMe 2 ) 2 I 2 (1.684(6) ). A similar behavior is observed for the torsion angle N1-B1-B2-N2 of the diboran(4)yl ligand, the value for 6 (À56.1(6)8) and 5 (À54.3(6)8) [12] being comparable but significantly smaller than that of B 2 A C H T U N G T R E N N U N G (NMe 2 ) 2 I 2 (N1-B1-N1'-B1': 77.0(6)8).…”

“…[12] However, the coordination of one boron center to platinum results in an elongation of the B1 À B2 bond by approximately 5 pm with respect to the diborane(4) precursor B 2 A C H T U N G T R E N N U N G (NMe 2 ) 2 I 2 (1.684(6) ). A similar behavior is observed for the torsion angle N1-B1-B2-N2 of the diboran(4)yl ligand, the value for 6 (À56.1(6)8) and 5 (À54.3(6)8) [12] being comparable but significantly smaller than that of B 2 A C H T U N G T R E N N U N G (NMe 2 ) 2 I 2 (N1-B1-N1'-B1': 77.0(6)8). This effect is most likely related to the steric requirements of the bulky platinum bisphosphine moiety.…”