Experimental Evaluation of (L)Au Electron‐Donor Ability in Cationic Gold Carbene Complexes

Abstract

Si NMR spectroscopy was employed to evaluate the electron donor properties of the (L)Au fragments in the cationic gold (β,β-disilyl)vinylidene complexes [(L)Au=C=CSi(Me) CH CH Si(Me) ] B(C F ) [L=P(tBu) o-biphenyl or NHC] relative to the p-substituted aryl group in the α-aryl-(β,β-disilyl)vinyl cations [(p-C H X)-C= CSi(Me) CH CH Si(Me) ] B(C F ) . Similarly, F NMR was employed to evaluate the σ- and π-electron donor properties of the (L)Au fragments in the neutral gold fluorophenyl complexes (L)Au(C H F) and in the cationic (fluorophenyl)methoxycarbene complexes [(L)AuC(OMe)(C H F)] SbF [L=P(tBu) o-biphenyl or IPr] relative to the p-substituted aryl group of the protonated monofluorobenzophenones [(p-C H X)(C H F)COH] OTf . The results of these studies indicate that relative to p-substituted aryl groups, the gold (L)Au fragments [L=P(tBu) o-biphenyl or NHC] are significantly more inductively electron donating and are comparable π-donors and for this reason, the extent of (L)Au→C1 electron donation in gold carbene complexes appears to exceed that provided by a p-(dimethyamino)phenyl group. Furthermore, the [L=P(tBu) o-biphenyl]Au fragment is a nominally stronger electron donor than the (IPr)Au fragment, and both are significantly more inductively electron donating than the (PPh )Au and [P(OMe) ]Au fragments.

Bond dissociation energies of carbonyl gold complexes: a new descriptor of ligand effects in gold(i) complexes?

“…The 16-MIC complex also exhibits the lowest value of electrostatic interaction for the complete series that confirms the high donation potential of this ligand. On the contrary, the 15-IPr complex bearing the IPr carbene is not a strong σ-donor ligand with a lower stabilization of electrostatic interaction than 1-tBu 42 (∆Eelect = -115.5 and -110.8 kcal/mol for complexes 1-tBu and 15-IPr respectively). However, the 15-IPr complex is less destabilized by Pauli repulsion with only 132.7 kcal/mol which explains the strength of the Au-CO bond.…”

Two Amphoteric Silver Carbene Clusters

“…The characteristic quinoid distortion in 12 a with short C1−C2 (1.433 Å) and C5−N1 (1.359 Å) bonds shows that the electron‐rich carbene backbone, rather than the metal center, largely accounts for the metastability of this complex. In contrast, the actual C1−Au1 carbene unit itself seems to lack significant π back‐donation: In this particular case, this bond has the exact same length [2.023(6) Å] as the bond between the gold atom and the IPr ligand, which is appreciated by the organometallic community for its poor π‐acceptor qualities. [28, 30}…”

Rhodium‐Catalyzed Cascade Synthesis of Benzofuranylmethylidene‐Benzoxasiloles: Elucidating Reaction Mechanism and Efficient Solid‐State Fluorescence

“…Once deprotonation of rhodium(I)-bisphenol complex K affords dearomatized allenylrhodiumc omplex L, [26] nucleophilic attack of the carbonyl oxygen to the silicon atom affords rhodium acetylide M,w hich is lower in energy than L (ca. 18 kcal mol À1 ), not throught he expected1 ,2-silicon migration butr ather through an unprecedented 1,5-silicon migration [27] via transition state LM_TS.T he interaction between the basic b-carbon of acetylide and the silicon atom then affords rhodium vinylidene A [28,29] via transition state MA_TS.R hodiumv inylidene A is transformedi nto h 3 -allenyl/propargyl-rhodium complex B through 1,3-carbon (alkyne) migration via transition state AB_TS.O nt he other hand, 1,2-silicon migration withoutd eprotonation would afford rhodiumv inylidene N via transition state KN_TS.S ubsequent deprotonation would also afford the rhodiumv inylidene A mentioned above.H owever,a ctivation energy of the step from L to M via LM_TS (6.5 kcal mol À1 )i sc a. 10 kcal mol À1 lower than that of the step from K to N via KN_TS (16.9 kcal mol À1 ), which suggests that the former pathway is more likely to occur.W ep reviously advocated that rhodiumv inylidene A might be generated from 1 through 1,2-siliconm igration.…”