Conversion of Tungsten(IV) Oxo−Alkyne Complexes to Oxo−Vinylidene Complexes

Abstract

A series of chiral tungsten(IV) oxo-alkyne complexes of the type Tp′W(O)(I)(RCtCR′) (R ) R′ ) H (1); R ) H, R′ ) Me (2); R ) R′ ) Me (3); R ) Me, R′ ) Ph (4); Tp′ ) hydridotris-(3,5-dimethylpyrazolyl)borate) has been prepared. These complexes were synthesized by reaction of Tp′W(O)(CO)(I) with Me 3 NO in the presence of an excess of alkyne. Phenylpropyne complex 4 was isolated as a 2:1 mixture of alkyne rotamers. For the propyne complex, a second route involving deprotonation of acetylene complex 1 followed by addition of MeI also produced complex 2. The oxidation pathway to 2 with Me 3 NO resulted in a 1:1.5 ratio of alkyne rotamers, while the elaboration of 1 via deprotonation/methylation gave 2 in a 9:1 ratio of alkyne rotamers. Addition of n-BuLi to propyne complex 2 resulted in deprotonation of the terminal acetylene site, and electrophile addition then produced the vinylidene complexes Tp′W(dCdCMe 2 )(O)(I) (5) and Tp′W[dCdC(Me)(H)](O)(I) (6) upon addition of MeI or HCl, respectively. X-ray structure determinations for alkyne complexes 2 and 4 and for vinylidene complex 5 are reported.

Towards Structural‐Functional Mimics of Acetylene Hydratase: Reversible Activation of Acetylene using a Biomimetic Tungsten Complex

“…This indicates that the system performs a9 0 8 8 alkyne rotation to ensure ideal orbital overlap,a sp reviously reported by Te mpleton and co-workers. [6,7] Thec rystallized isomers of 2 and 3 differ in the arrangement of ligands.AN,Ntrans arrangement is found in complex 2,w hereas 3 features an S,S-trans geometry.T his variation in the ligand arrangements within the complexes further shows the high flexibility and adaptability of our ligand system, features which we have also recently observed for related Pd II complexes. [20] We have successfully developed and fully characterized an ew,b iomimetic system which can not only stabilize tungsten-acetylene adducts,b ut is also capable of the reversible activation of acetylene.R elease and activation of acetylene can be easily controlled by visible light.…”

“…[4,5] About 20 years later, the scorpionate complexes [Tp'WOI(C 2 H 2 )] and [Tp'WOI-(C 2 H 2 )] (Tp' = hydridotris(3,5-dimethylpyrazolyl)borate)] were used to examine vinyl-and vinylidene-tungsten bonding. [6][7][8] Theo nly structural-functional model of AH was reported by Sarkar et al [9,10] Originally [Et 4 N] 2 [WO(mnt) 2 ] (mnt = malonitrile) was designed to model W-dependent aldehyde ferredoxin oxidoreductase. [9] Thec omplex was also found to perform approximately nine turnovers of acetylene hydration.…”

Structural Mimics of Acetylene Hydratase: Tungsten Complexes Capable of Intramolecular Nucleophilic Attack on Acetylene

“…[6][7][8] Amongt he latter,t he scorpionate complex [WO(C 2 H 2 )Tp'I] (Tp' = hydridotris(3,5-dimethylpyrazolyl)borate) binds both substrates, C 2 H 2 and H 2 O, upon halogen abstraction, whereas the recents tructural analogue [WO(C 2 H 2 )(S-Phoz) 2 ]( S-Phoz = 2-(4'4'-dimethyloxazoline-2'-yl)thiophenolate)e xhibitsr eversible C 2 H 2 binding. [7,8] The only structural-functional model [Et 4 N] 2 [WO(mnt) 2 ]( mnt = malonitrile) was reported to perform nine catalytic turnovers, whereas no WÀC 2 H 2 adduct could be isolated or spectroscopically observed. [9,10] However,r ecent attempts to reproduce these resultsf ailed, which questions the existence of as tructural-functionalm odel for AH.…”

“…For the preparation of acetylene complexes with the SPy and SPn ligands, ap rocedure previously employed for [W(CO)(C 2 H 2 )(S-Phoz) 2 ]w as followed. [8,14] Thus, in af irst step, previously reported [W 2 (CO) 7 Br 4 ] [15] was convertedt o [W(CO) 3 (MeCN) 2 Br 2 ], [16] which was subsequently reactedw ith two equivalents of the sodium salt of the respective ligand in dichloromethane. The use of SPy gave the tris-carbonylc om- Figure 1.…”

“…It further displays the typical parallel arrangemento ft he CO and the C 2 H 2 ligand. [7,23] The structures of 4 and 5 revealed that the Na tom of the heterocycle acted as intramolecular nucleophile. The S,N-trans ligand arrangementi sc onserved during insertion of acetylene into the WÀNb ond giving the corresponding S,Ctrans complexes.…”