T-Shaped Gold→Stiborane Complexes as Carbophilic Catalysts: Influence of the Peripheral Substituents

Abstract

As part of our efforts toward the discovery of new late transition metal catalysts, we synthesized [(o-(Ph 2 P)C 6 H 4 ) 2 (o-C 6 Cl 4 O 2 )SbPh)Au] + (3 + ) and [(o-(iPr 2 P)-C 6 H 4 ) 2 (o-C 6 Cl 4 O 2 )SbPh)Au] + (4 + ), two cationic bis-(phosphino)gold stiborane complexes, which were isolated as their hexafluorophosphate salts and fully characterized.Structural and computational studies indicate that the cores of these two complexes are almost structurally and electronically identical. Despite these similarities, these two complexes exhibit different catalytic activities in the hydroamination of phenylacetylene using anilines or in the cyclization of N-(prop-2-yn-1-yl)benzamide. Indeed, whereas 3 + catalyzes both reactions, we found that 4 + is inactive. The data collected on these two complexes suggest that the origin of this contrasting behavior is steric, rather than electronic, with the relatively bulky iPr 2 P ancillary ligands blocking access to the reactive gold center.

A Germylene Supported by Two 2‐Pyrrolylphosphane Groups as Precursor to PGeP Pincer Square‐Planar Group 10 Metal(II) and T‐Shaped Gold(I) Complexes

“…Its XRD structure ( Figure 6) confirmed that the molecule arises from the insertion of the Ge atom of 1 into the AuÀCl bond of the gold precursor, resulting in ac omplex containing aP GeP pincer chloridogermyl ligand attached in aT -shape mode to ag old(I) atom (the originalT HT ligand was displaced from the gold atom). Comparing the AuÀEd istances in ZEZ-pincer T-shaped gold(I) complexes (Figure7), the Au1ÀGe1 distance of 5,2 .7639 (7) , is similar to the AuÀSb distances of the CSbC complexes of Gabbaï et al,2 .7694(8)a nd 2.7486 (7) , [23] much shorter than the AuÀSb distances of the PSbP complexes of Gabbaï et al, which are in the range 2.995-2.932 , [24] and longert han the AuÀBd istance of the PBP complex of Inagaki et al, [25] 2.521 (2) ,t he AuÀNd istances of the CNC complexes of Bezuidenhout et al,2 .325 (2) for Ar = 2,6-bis(isopropyl)phenyl (Dipp) and (2),P t1ÀP2 2.360 (2),P t1ÀGe1 2.3140 (8), Pt1ÀCl2 2.364(2), Ge1ÀCl1 2.209(2), Ge1ÀN1 1.864 (7), Ge1ÀN2 1.852 (7);N1-Ge1-N2 101.4 (3), N1-Ge1-Pt1 122.3 (2), N2-Ge1-Pt11 17.9(2), N1-Ge1-Cl1 101. 3(2),N 2-Ge1-Cl1 100.0(2), Cl1-Ge1-Pt1 110.72 (6), Ge1-Pt1-Cl2 169.10 (6), P1-Pt1-P2 168.84 (7), P1-Pt1-Ge1 90.79 (5), P2-Pt1-Ge1 88.61 (5),P1-Pt1-Cl2 91.70 (7),P2-Pt1-Cl2 90.97(7).…”

“…The AuÀGe distances of "normal" (not T-shaped) mononuclear complexes containing germyl ligands are also shorter than that of complex 5,n amely,i nt he range of 2.362-2.423 . [28] It should be noted that T-shaped pincer gold(I) complexes are very rare, the only examples currentlyk nown being those depicted in Figure 7 [23][24][25][26][27] (most tricoordinate gold(I) complexes are trigonal planar [29] ).…”

“…It should be emphasized that this situation sharply contrasts with that found for all T-shaped gold(I) complexes of Gabbaï et al (Figure 7), in which the AuÀSb attachment is also weak (ÀDE (2) in the range 59-28 kcal mol À1 )b ut corresponds to an Au!Sb donor-acceptori nteraction (wheret he gold is the donora tom). [23,24] Aiming ats hedding some light on the influenceo ft he pincerl igand effect on the AuÀGe distance of complex 5,w e modelled by DFT methods as ystem in whicht he Au atom of a [Au(kP-PMetBu 2 ) 2 ] + ion approaches the Ge atom of a[ GeCl-(pyrMe) 2 ] À ion. It should be noted that the pincer ligand effect is completely suppressed in this model system because the pyrrolyl (pyr) and phosphanyl (PtBu 2 )m oieties, which are spanned by am ethylene group in complex 5,a re attached to methylg roups in the models ystem.I nterestingly,t he resulting optimized structure( [Au{kGe-GeCl(pyrMe) 2 }(kP-PMetBu 2 ) 2 ], Figure S34 in the Supporting Information) corresponded to a trigonal-planar tricoordinate gold(I) complex having aG e ÀAu distance of 2.543 (0.221 shorter than that of complex 5!).…”

An Antimony(V) Dication as a Z‐Type Ligand: Turning on Styrene Activation at Gold

“…[1i,j] Examples that illustrate the tunability of these ligand systems include double-decker complexes of type I where variation of the Group 13 element allows for the precise control of the Ni-E interaction [4] as well as complexes of type II where the redox state of the antimony center can be used to adjust the strength of the Au-Sb interaction ( Figure 1). [5] Based on the principle that cationic main group compounds are more Lewis acidic than their neutral counterparts, [6] we have been interested in an approach whereby anion abstraction serves to enhance the s-accepting properties of the Z-type ligand. [7] We demon-strated this idea in the case of complex III which, upon conversion into IV by fluoride anion abstraction, became catalytically active as ar esult of as tronger Pt!Sb interaction.…”

“…We were also eager to test whether [4][NTf 2 ] 2 could be generated in situ, starting from [2a] [Cl].W efound that when generated in this way, [4][NTf 2 ] 2 showed acatalytic activity in the hydroamination of styrene that is almost identical to that observed when [3][NTf 2 ] 2 is used as ap recatalyst (entries [5][6][7][8]. This reaction is not activated by complex [3] 2+ or AgNTf 2 alone.When5mol %HNTf 2 was employed as acatalyst, only 16 %o fh ydroamination product was formed, and formation of polystyrene was observed.…”