Reactivity of Silyl-Substituted Heterobimetallic Iron–Platinum Hydride Complexes towards Unsaturated Molecules, I Alkyne Insertions into the Platinum-Hydride Bond, Phosphane-Induced σ-Alkenyl–μ-Vinylidene Rearrangements and Formation of μ-Isonitrile Complexes

Abstract

The heterobimetallic hydride complexes [(OC)3Fe{Si(OMe)3}(μ‐Ph2PXPPh2)Pt(H)(PR3)] (1a: X = CH2, PR3 = PPh3; 1b: X = NH, PR3 = PPh3; 1c: X = CH2, PR3 = PMePh2) have been prepared by the oxidative addition of [(OC)3Fe(H){Si(OMe)3}(η1‐Ph2PXPPh2)] to [Pt(H2CCH2)(PPh3)2] or by reaction of K[(OC)3Fe{Si(OMe)3}(η1‐dppm)] with trans‐[Pt(Cl)(H)(PPh3)2]. The solid‐state structure of compound 1b has been determined by single‐crystal X‐ray diffraction. 1‐Alkynes such as methylpropiolate or phenylacetylene insert in a regiospecific manner into the Pt–H bond of 1 to yield the σ‐alkenyl complexes [(OC)3Fe{μ‐Si(OMe)2(OMe)}(μ‐Ph2PXPPh2)Pt{C(R)=CH2}] (2a: X = CH2, R = CO2Me; 2b: X = NH, R = CO2Me; 3a: X = CH2, R = Ph). Addition of the Pt–H bond of 3a across the triple bond of [D1]phenylacetylene affords [(OC)3Fe{μ‐Si(OMe)2(OMe)}(μ‐dppm)Pt{C(Ph)=C(D)H}] (3a*) having the deuteron trans to platinum (cis addition). This insertion reaction is accompanied by dissociation of the platinum‐bonded PR3 ligand and saturation of the vacant coordination site by a dative μ‐η2‐Si–O→Pt interaction. When 3 is treated with PR3 again, a subsequent phosphane‐induced rearrangement leading to vinylidene‐bridged complexes [(OC)3Fe{μ‐CC(H)R′}(μ‐Ph2PXPPh2)Pt(PR3)] (4a: X = CH2, R′ = Ph, PR3 = PPh3; 4b: X = NH, R′ = Ph, PR3 = PPh3; 4c: X = CH2, R′ = Ph, PR3 = PMePh2; 4d: X = CH2, R′ = p‐tolyl, PR3 = PPh3) occurs. Upon purging a solution of 3a with carbon monoxide, the labile CO adduct [(OC)3Fe{Si(OMe)3}(μ‐dppm)‐Pt(CO){C(Ph)=CH2}] 5a is formed, addition of 2,6‐xylyl isocyanide to 2a and 3a affords the isonitrile adducts [(OC)3Fe{Si(OMe)3}(μ‐dppm)Pt(CNxylyl){C(R)=CH2}] (5b: R = CO2Me; 5c: R = Ph), respectively. When hydride complex 1a is allowed to react with stoichiometric amounts of aromatic isonitriles, formal elimination of HSi(OMe)3 occurs, yielding the heterodinuclear isonitrile‐bridged complexes [(OC)3Fe(μ‐C=N‐R)(μ‐dppm)Pt(PPh3)] (6a: R = 2,6‐xylyl; 6b: R = o‐anisyl; 6c: R = p‐anisyl; 6d: R = p‐C6H4NH2) and the bis(isonitrile) complexes [(OC)2(RN≡C)Fe(μ‐C=N–R)(μ‐dppm)Pt(PPh3)] (7a: R = 2,6‐xylyl; 7b: R = p‐anisyl). Single‐crystal X‐ray diffraction studies perfomed on 6a and 6b reveal that the molecular structures of these μ‐isonitrile complexes closely resemble the μ‐vinylidene complexes 4. The two metal centers are bridged in a symmetric manner by strongly bent CNR ligands, the aromatic groups R being oriented towards the Fe(CO)3 moiety. Electrophilic addition of HBF4 to the basic nitrogen atom of the μ‐CNR ligand transforms 6 to the cationic μ‐aminocarbyne complexes [(OC)3Fe{μ‐CN(H)R}(μ‐dppm)Pt(PPh3)][BF4] (8a: R = 2,6‐xylyl; 8b: R = p‐anisyl; 8c: R = p‐C6H4NH2).

Reactivity of silyl-substituted heterobimetallic iron–platinum hydride complexes: Part III. Alkyne insertions into the platinum–hydride bond and competition between μ-vinylidene and dimetallacyclopentenone formation

“…With hexafluorobutyne as substrate, subsequent elimination of the silyl group and intermolecular CO-trapping yielded the 1,2-dimetallacyclobutene complex [(OC) 3 Fe(l-dppm)(l-CF 3 C@CCF 3 )Pt(CO)] [9]. In the case of phenyl-and p-tolylacetylene, a phosphane-induced rearrangement reaction transformed the initial r-alkenyl complexes to l-vinylidene complexes [(OC) 3 Fe{l-C@C(H)Ar}(l-dppm)Pt(PR 3 )] [10]. For comparison, we were curious to study the behavior of less reactive aliphatic terminal 1-alkynes.…”

“…There has also been great interest in the chemistry of heterobimetallic complexes towards alkynes, since a cooperative effect between the two adjacent metal centers often facilitates the activation of the organic substrate [7]. In previous papers we have studied the insertion of aromatic terminal alkynes and activated alkynes bearing strongly electron-withdrawing CF 3 -substituents into the Pt-H bond of the heterobimetallic hydride complex [(OC) 3 Fe{Si(OMe) 3 }(l-dppm)Pt(H)(PR 3 )] (1) [8][9][10]. Insertion afforded first r-alkenyl complexes [(OC) 3 Fe{l-Si(OMe) 2 (OMe)}(l-dppm)Pt(RC@C(H)R 0 )] (R = Ar, R 0 = H; R = CF 3 , R 0 = H; R = R 0 = CF 3 ) with concomitant dissociation of PPh 3 .…”

Reactivity of silyl-substituted heterobimetallic iron–platinum hydride complexes towards unsaturated molecules: Part II. Insertion of trifluoropropyne and hexafluorobutyne into the platinum–hydride bond

“…Pt cycle is formed via a dative interaction of a methoxy group of the trimethoxysilyl ligand; due to the dissymmetric environment around Pt, three distinct resonances for the methoxy groups are found at d 3.72, 3.70 and 3.60, the latter being splitted in a doublet by a 4 J(P-H) coupling of 2 Hz. The finding that insertion of hexafluorobutyne into the Pt-H bond of 1 occurs exclusively with a trans-stereochemistry about the resulting alkenyl complex needs some comments. By a labelling experiment using deuterated phenylacetylene, we have shown that the deuteron is located cis to Pt, consistent with a cis-addition of 1 across the Ph-C"C-D triple bond [15] 3 Fe Pt 3 Fe Pt 3 Fe Pt…”

“…Surprisingly, no spectroscopic change was noticed upon exposing a solution of 3a under a CO atmosphere for 3h, excluding formation of [(OC) 3 Fe{Si(OMe) 3 [15]. This inertness in the case of 3a may be explained by a strengthening of the dative Si-O !…”

“…In the course of our investigations on the activation of small molecules by heterobimetallics, we recently examined the insertion of phenylacetylene and p-tolylacetylene into the Pt-H bond of heterodinuclear ironplatinum hydride complexes [(OC) 3 Fe{Si(OMe) 3 } (l-Ph 2 PXPPh 2 )Pt(H)(PPh 3 )] (1a X = CH 2 ; 1b X = NH) [15]. The influence of the second adjacent metal center close to a square planar platinum(II) moiety on the regio-and site selectivity of this important reaction was of special interest.…”