Thallium(I) as a Coordination Site Protection Agent: Preparation of an Isolable Zero‐Valent Nickel Tris‐Isocyanide

Fox, Brian J.; Millard, Matthew D.; DiPasquale, Antonio G.; Rheingold, Arnold L.; Figueroa, Joshua S.

doi:10.1002/anie.200806007

Cited by 71 publications

(63 citation statements)

References 53 publications

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“…15 Structural characterization of Ni(CNAr Dipp2 ) 3 on crystals grown from MeCN/C 7 H 8 revealed 51 a trigonal-planar complex, as is expected for a zerovalent Ni center ligated by three strongly π-acidic ligands ( Figure 4). 11À13 The primary coordination sphere of Ni(CNAr Dipp2 ) 3 closely matches that of the dimesityl derivative 24 Ni(CNAr Mes2 ) 3 and is uncongested in the vicinity of the Ni center because of the two-atom separation from the m-terphenyl group. However, a more crowded steric environment in Ni(CNAr Dipp2 ) 3 relative to Ni(CNAr Mes2 ) 3 is indicated by its "picket fence" arrangement of the three Ar Dipp2 units.…”

Section: ' Results and Discussionmentioning

confidence: 91%

“…This shift in energy is consistent with the Tl ligand functioning as a Lewis acid with respect to the Ni center and thus decreases the electron density available for π-back-donation to the CNAr Dipp2 ligands. 24 To this end, a statistically significant lengthening of the CÀNi bond lengths is observed in [TlNi (CNAr Dipp2 ) 3 ]OTf relative to three-coordinate Ni(CNAr Dipp2 ) 3 (1.844(2) Å (av) Organometallics ARTICLE vs 1.819(10) Å (av), respectively) and thus further suggests diminished NiÀisocyanide π-back-bonding in the presence of the coordinated Tl center. Notably, addition of THF to a C 6 D 6 solution of [TlNi(CNAr Dipp2 ) 3 ]OTf distrupts the NiÀTl interaction and regenerates Ni(CNAr Dipp2 ) 3 as assayed by 1 H NMR and IR spectroscopy.…”

Section: ' Results and Discussionmentioning

confidence: 94%

“…The closest C aryl ÀTl contact in [TlNi (CNAr Dipp2 ) 3 ]OTf is 3.206 Å, thus suggesting that the CNAr Dipp2 ligand periphery does not aid the NiÀTl interaction to any significant extent in the solid state. Indeed, the unsupported NiÀTl bond length in [TlNi (CNAr Dipp2 ) 3 ]OTf of 2.6765(6) Å is only slightly longer than that found in the CNAr Mes2 analogue, 24 [TlNi(CNAr Mes2 ) 3 ]OTf (d(NiÀTl) = 2.6105(11)Å), but is shorter than those found in the COD derivatives [TlNi(COD)(CNAr Mes2 ) 2 ]OTf and [TlNi(COD)(CNAr Mes2 ) 2 ] BAr F 4 (3.0235(4) and 2.853(2) Å, respectively). We believe this difference stems from the absence of a ligand trans to the Tl center.…”

Section: ' Results and Discussionmentioning

confidence: 94%

“…26 However, this fact may simply reflect the inability of a transition-metal center to accommodate three mutually cis-CNAr Dipp2 ligands While unnecessary for its synthesis, Ni(CNAr Dipp2 ) 3 is capable of forming reverse dative σ-interactions with Tl(I) centers. 24 3 ]OTf (4) as determined by X-ray diffraction (Scheme 2, Figure 6). Such reactivity is consistent with the electronic structure expected for Ni (CNAr Dipp2 ) 3 , whereby its d z 2 HOMO allows it to function as a σ-type Lewis base.…”

Section: ' Results and Discussionmentioning

confidence: 99%

“…Importantly, this property enabled the synthesis of Ni-(CNAr Dipp2 ) 3 without the need for a coordination-site protection as had been employed previously for the synthesis of the dimesityl derivative, Ni(CNAr Mes2 ) 3 . 24 As hoped, Ni(CNAr Dipp2 ) 3 shares geometric and electronic structure attributes with the unstable binary carbonyl Ni(CO) 3 . This similarity is most well illustrated by the ability of Ni-(CNAr Dipp2 ) 3 to bind Tl(I) in a reverse-dative σ-donation fashion.…”

Section: ' Concluding Remarksmentioning

confidence: 98%

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Protecting-Group-Free Access to a Three-Coordinate Nickel(0) Tris-isocyanide

et al. 2011

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It is well established that the active intermediate in reactions mediated by nickel tetracarbonyl (Ni(CO) 4 ) is the three-coordinate complex Ni(CO) 3 . 1À4 This coordinatively unsaturated binary carbonyl is formed by CO dissociation from its fourcoordinate, 18-electron precursor and is active toward ligand association 1À4 and oxidative addition 5À7 reactions. While too reactive to be isolated or observed in the condensed phase, pioneering gas-phase and matrix-isolation studies by Turner, DeKock, and Burdett succeeded in photolytically synthesizing and fully characterizing Ni(CO) 3 . 8À10 Along with these experiments, early theoretical predictions based on molecular orbital and angular overlap methods corroborated the fact that d 10 Ni(CO) 3 adopts a trigonal-planar coordination geometry. 11À13 This geometry is similar to three-coordinate, Ni(0) trisphosphine complexes (i.e., Ni(PR 3 ) 3 ), which are long known 14 and have been isolated when encumbering phosphines are employed. 15,16 Despite sharing three-coordinate, trigonal-planar geometries, Ni(CO) 3 is electronically distinct from Ni(PR 3 ) 3 complexes. This is a result of the stabilization of Ni-based, π-symmetry orbitals (e 0 and e 00 in D 3h symmetry) by back-donation to the CO ligands. Accordingly, the HOMO of D 3h -symmetric Ni(CO) 3 is d z 2 (a 1 0 ) in parentage, rather than the degenerate e 0 set (x 2 À y 2 , xy), as is widely accepted for Ni(PR 3 ) 3 complexes (Figure 1). 17 Indeed, stabilization of both the e 0 and e 00 orbital sets by the cylindrically symmetric CO π* orbitals serves to energetically isolate the Ni d z 2 orbital in Ni(CO) 3 (Figure 1) and renders the complex isolobal to σ-type Lewis bases such as phosphines and amines. In this respect, Ni(CO) 3 is also differentiated from the "planar" form of trisethylene Ni(0) (Ni(C 2 H 4 ) 3 ), 18 which possesses only the in-plane, e 0 -symmetry π-back-bonding interaction. However, the weaker π-acidity of ethylene relative to CO does not allow for an e 0 orbital Figure 1. (top) Qualitative molecular orbital diagrams for the D 3h -symmetric NiL 3 complexes Ni(C 2 H 4 ) 3 (left), Ni(PMe 3 ) 3 (center), and Ni(CO) 3 (right), reflecting the effect of π-back-donation on the d-orbital splitting pattern. (bottom) DFT-calculated HOMO for Ni(CO) 3 (left) and Ni(CN Me) 3ABSTRACT: Details are presented regarding a convenient synthesis of the nickel trisisocyanide complex Ni(CNAr Dipp2 ) 3 (Ar Dipp2 = 2,6-(2,6-[i-Pr] 2 C 6 H 3 ) 2 C 6 H 3 ). A previous synthesis of a Ni tris-isocyanide complex relied on a Tl(I) coordination-site protection strategy to discourage the formation of a tetrakis-isocyano complex. However, protectinggroup-free access to Ni(CNAr Dipp2 ) 3 is enabled by the encumbering m-terphenyl isocyanide CNAr Dipp2 . Treatment of Ni(COD) 2 with CNAr Dipp2 affords Ni(COD)-(CNAr Dipp2 ) 2 , which is readily oxidized to NiI 2 (CNAr Dipp2 ) 2 upon addition of I 2 . Reduction of NiI 2 (CNAr Dipp2 ) 2 with Mg metal generates Ni(CNAr Dipp2 ) 3 and does not require the addition of a third equivalent of C...

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Section: ' Results and Discussionmentioning

confidence: 91%