Mark W. Whiteley

Synthetic and electrochemical studies on alkynyl complexes of iron and ruthenium

Cyclic voltammetric studies on a series of alkynyl complexes [M(CCR)L2(η- C5R′5)] (M = Fe or Ru; R = Ph, Bun or But; L = CO or P-donor ligand; R′ = H or Me) reveal a one-electron oxidation at a glassy carbon electrode in dichloromethane. The chemical reversibility of the oxidation process is dependent upon all four variables (M, L, R and W) considered in this investigation.

Ligand-centred coupling of the alkynyl radical cations [Mo(CCR)(Ph2PCH2CH2PPh2)(η-C7H7)]+ (R = Ph or Bun: crystal structure of the dimeric product [Mo2(Ph2PCH2CH2PPh2)2(η-C7H7)2(μ-C4R2)][PF6]2 (R = Ph)

The radical cations [Mo(CCR)(dppe)(η-C7H7)]+ (R = Ph or Bun); dppe = Ph2PCH2CH2PPh2) undergo coupling at Cβ of the alkynyl ligand to afford the divinylidene-bridged, dimeric products [Mo2(dppe)2(η-C7H7)2(μ-C4R2)]2+, characterised crystallographically for R = Ph.

The X-ray crystal structures of [Mo(CCPh)(Ph2PCH2CH2PPh2)(η-C7H7)] and [Mo(CCPh)(Ph2PCH2CH2PPh2)(η-C7H7)] [BF4] (C7H7 = cycloheptatrienyl): an investigation of metalalkynyl bonding

Abstract Single crystal X-ray diffraction studies have been carried out on the cycloheptatrienylmolybdenum alkynyl complexes [Mo(C CPh)(dppe)(η-C7H7)] (1) and [Mo(C CPh)(dppe)(η-C7H7)][BF4] (2-[BF4]) (dppe = Ph2PCH2CH2PPh2) to investigate the structural effects of one-electron oxidation of 1. The major structural alterations resulting from oxidation of 1 to 2-[BF4] are an increase of 0.061(2)Ain the mean Mo phosphorus separation and a decrease of 0.071(10)Ain the Mo alkynyl carbon bond length. The mean Mo to cycloheptatrienyl carbon distance and the alkynyl C C bond length are virtually unchanged. These observations are consistent with a metal-based redox site in 1 and, in conjunction with the results of electrochemical and infrared studies, suggest that the alkynyl ligand in 1 acts predominantly as a σ-donor to molybdenum with any contribution to the metal alkynyl bond from a dπ (metal) → π* (alkynyl) interaction being relatively insignificant in this particular example.

Spectroscopic investigations on the structure and fluxionality of the trihaptocycloheptatrienyl complexes [MX(CO)2(LL)(η3-C7H7)] (M Mo, W; X I, Cl; LL bisphosphine or diamine) and synthesis of the tetracyanoethene adducts [WI(CO)2{Ph2P(CH2)nPPh2}{η3-C9H7(CN)4}] (n = 1 or 2)

Abstract Spectroscopic investigations, including 31 P, 1 H and 13 C NMR studies, on the formally 6-coordinate bisphosphine complexes [MX(CO) 2 {Ph 2 P(CH 2 ) n PPh 2 }(η 3 -C 7 H 7 )] (M  Mo, W; X  I, Cl; n = 2 (dppe), n = 1 (dppm); C 7 H 7  cycloheptatrienyl) reveal a structure with no molecular plane of symmetry in which inequivalent P-donor atoms are arranged cis-cis and cis-trans to the two mutually cis -carbonyl groups. The dppe complexes exhibit a fluxional process which interconverts inequivalent phosphorus environments. Low temperature 1 H and 13 C NMR studies on the diamine derivatives [MCl(CO) 2 (H 2 NCH 2 CH 2 NH 2 )(η 3 -R)] (M  Mo, W, R  C 7 H 7 ; M  Mo, R  C 3 H 5 (allyl)) imply that the non-symmetric structure of the bisphosphine analogues is adopted. The adducts [WI(CO) 2 {Ph 2 P(CH 2 ) n -PPh 2 } {η 3 -C 9 H 7 (CN) 4 }] ( n = 1 or 2) are formed by tetracyanoethene addition to the trihapto-bonded cycloheptatrienyl ring of the tungsten complexes [WI(CO) 2 -{Ph 2 P(CH 2 ) n PPh 2 }(η 3 -C 7 H 7 )] ( n = 1 or 2).

The chemistry of cycloheptatrienyl complexes of molybdenum and tungsten: synthesis and redox chemistry of some phosphine-and phosphite-substituted halide and acetonitrile derivatives

Abstract Reaction of [Mo(η-C 6 H 5 Me)(η-C 7 H 7 )][PF 6 ] (C 6 H 5 Me = toluene) with two equivalents of P(OMe) 3 in refluxing acetonitrile affords [Mo(NCMe){P(OMe) 3 } 2 (η-C 7 H 7 )][PF 6 ], which is a precursor for the neutral complex [MoI{P(OMe) 3 } 2 (η-C 7 H 7 )] ( 2 ) and the radical cation [MoCl{P(OMe) 3 } 2 (η-C 7 H 7 )][PF 6 ] ( 3 ). Treatment of [WI(CO) 2 (η-C 7 H 7 )] with PPh 3 gives [WI(CO)(PPh 3 )(η-C 7 H 7 )] ( 6 ), which is a starting material for the synthesis of [W(CO)(dppe)(η-C 7 H 7 )][PF 6 ] (dppe = Ph 2 PCH 2 CH 2 PPh 2 ) and hence [W(NCMe)(dppe)(η-C 7 H 7 )][PF 6 ] ( 9 ). Reaction of 9 with LiCl gives a mixture of [WCl(dppe)(η-C 7 H 7 )][PF 6 ] ( 14 ) and [WCl(dppe)(η-C 7 H 7 )]. Cyclic voltammetric studies on 2 , 3 , 6 , 9 , [Mo(NMe)(dppe)(η-C 7 H 7 )][PF 6 ] ( 10 ), and 14 reveal reversible one-electron transfer processes, and [MoI{P(OMe) 3 } 2 (η-C 7 H 7 )][BF 4 ] ( 4 ), [MoCl{P(OMe) 3 } 2 (η-C 7 H 7 )] ( 5 ) and [M(NCMe)(dppe)(η-C 7 H 7 )][PF 6 ] 2 ( 11 , M = W; 12 , M = Mo) have been isolated by use of chemical redox reagents. The radicals 3 , 4 , 11 , 12 and 14 have been studied by ESR spectroscopy.

The synthesis of ring-substituted cycloheptatrienyl complexes [M(CO)3(η7-C7H6R)]+ (M = Cr, Mo or W; R = Me, tBu, C6H4F-p or CCPh)

Abstract The relative merits of various routes to ring-substituted cycloheptatrienyl complexes [M(CO) 3 (η 7 -C 7 H 6 R)] + (M = Cr, Mo or W) have been explored. Substitution at a metal coordinated C 7 H 7 ring is effected via addition, thermal rearrangement and subsequent H − abstraction. Thus reaction of [Mo(CO) 3 (η 7 -C 7 H 7 )] + with NaOMe gives [Mo(CO) 3 {η 6 -(7- exo -OMe)C 7 H 7 }], which affords substituted cycloheptatriene complexes [Mo(CO) 3 {η 6 -(7- exo -R)C 7 H 7 }] [R = Me ( 1 ); t Bu ( 2 ); C 6 H 4 -F- p ( 3 )] by reaction with RMgX; direct addition of CCPh to [M(CO) 3 (η 7 -C 7 H 7 )] + to give [M(CO) 3 {η 6 -(7- exo -CCPh)C 7 H 7 }] [M = Cr ( 4 ); M = Mo ( 5 )] is brought about by reaction with alkynyl cuprate reagents. Thermolysis of 1–4 gives isomeric mixtures of rearranged cycloheptatriene complexes [M(CO) 3 {η 6 -( n -R)C 7 H 7 }] ( n = 1, 2 or 3), which contain a CH 2 ring carbon with an exo hydrogen accessible to H − abstraction by Ph 3 C + to yield the ring-substituted cycloheptatrienyl complexes [M(CO) 3 (η 7 -C 7 H 6 R)] + [M = Mo; R = Me ( 7 ); t Bu ( 8 ); C 6 H 4 -F- p ( 9 ); M = Cr, R = CCPh ( 10 )]. Alternatively, substituted cycloheptatrienes C 7 H 7 R and cycloheptatrienyl ions C 7 H 6 R + may be coordinated directly to [M(CO) 3 (NCMe) 3 ]. Reaction of 7-Me-C 7 H 7 with [M(CO) 3 (NCMe) 3 ] (M = Cr, Mo or W) in THF affords [M(CO) 3 {η 6 -(7-Me)C 7 H 7 }] as a (metal dependent) exo / endo isomeric mixture at C(7). The reaction of the cycloheptatrienyl ions C 7 H 6 R + (R = Me, t Bu, C 6 H 4 -F- p , OCPh) with [M(CO) 3 (NCR′) 3 ] (M = Mo, R′= Me; M = W, R′=′Pr) proceeds at room temperature in THF or CH 2 Cl 2 and provides convenient syntheses of 7 , 8 , 9 , [Mo(CO) 3 {η 7 -C 7 H 6 (CCPh)}] + ( 11 ) and [W(CO) 3 (η 7 -C 7 H 6 R)] + [R = Me ( 12 ); C 6 H 4 -F- p ( 13 )]. Complexes 7, 8, 9, 12 and 13 are useful starting materials for investigation of the chemistry of ring-substituted cycloheptatrienyl complexes, as exemplified by the syntheses of [MI(CO) 2 (η 7 -C 7 H 6 Me)] [M = Mo ( 14 ); M = W ( 15 )] and the sandwich complex [Mo(η 6 -toluene)(η 7 -C 7 H 6 Me)] + ( 16 ).

The chemistry of cycloheptatrienyl complexes of molybdenum and tungsten: synthesis and substitution chemistry of some new carbonylacetonitrile derivatives

Abstract Reaction of [Wl(CO) 2 (η-C 7 H 7 ) with Ag[BF 4 ] in acetonitrile yields the trihaptocycloheptatrienyl complex [W(CO) 2 (NCMe) 3 (η-C 7 H 7 )[BF 4 ] ( 2 ), which in CH 2 Cl 2 is converted into [W(CO) 2 (NCMe)(η-C 7 H 7 )][BF 4 ] ( 1 ). A similar reaction sequence is observed starting from [MoI(CO) 2 (η-C 7 H 7 ))] and Ag[BF 4 ], but a mixture of [Mo(CO) 2 (NCMe)(η-C 7 H 7 )][BF 4 ] ( 3 ) and a species formulated as [Mo(CO) 2 -(NCMe) 3 (η-C 7 H 7 )][BF 4 ] ( 4 ) is obtained in acetonitrile. Treatment of CH 2 Cl 2 solutions of 1 or 3 with phosphorus-donor ligands PR′ 3 (R′  OMe or Bu n ) or Ph 2 PCH 2 PPh 2 gives, respectively, [M(CO) 2 (PR′ 3 )(η-C 7 H 7 )][BF 4 ] and the pendent phosphine complexes [M(CO) 2 (Ph 2 PCH 2 PPh 2 )(η-C 7 H 7 )][BF 4 ] ( 11 , M  W; 12 , M  Mo). Dissolution of 11 in MeCN affords the chelated phosphine-trihaptocycloheptatrienyl derivative [M(CO) 2 (NCMe)Ph 2 P(CH 2 ) n PPh 2 (η-C 7 H 7 )][BF 4 ] (M = W, n = 1); analogous complexes (M = Mo or w, n = 2) result from reaction of 2 pr 3 with Oh 2 P(CH 2 ) 2 PPh 2 in MeCN. Ultraviolet irradiation of 3 in MeCN yields [Mo(CO)(NCMe) 2 (η-C 7 H 7 )][BF 4 ].

Synthesis and redox properties of the cycloheptatrienylmolybdenum complexes [MoX(N–N)(η-C7H7)]z+, (N–N=2,2′-bipyridine or 1,4-But2-1,3-diazabutadiene; z=0, X=Br or Me; z=1, X=NCMe, CNBut or CO)

Abstract The complexes [MoBr(N–N)( η -C 7 H 7 )] (N–N=2,2′-bipyridine (bipy), 1a ; N–N=1,4-Bu t 2 -1,3-diazabutadiene (Bu t -dab), ( 1b ) have been prepared by reaction of [MoBr(CO) 2 ( η -C 7 H 7 )] with N–N in refluxing toluene. Treatment of 1a or 1b with MeLi affords [MoMe(N–N)( η -C 7 H 7 )] (N–N=bipy or Bu t -dab). The acetonitrile complexes [Mo(NCMe)(N–N)( η -C 7 H 7 )][PF 6 ], generated by reaction of [Mo( η -C 6 H 5 Me)( η -C 7 H 7 )][PF 6 ] with N–N in NCMe, are precursors to [MoX(N–N)( η -C 7 H 7 )][PF 6 ] (X=CNBu t or CO; N–N=bipy or Bu t -dab), through substitution of NCMe by X. Cyclic voltammetric studies reveal that each of the complexes [MoX(N–N)( η -C 7 H 7 )] z + (X=Me, Br, NCMe or CNBu t ; N–N=bipy or Bu t -dab) exhibits a reversible one-electron oxidation and the 17-electron radicals derived from 1a , b and [Mo(CNBu t )(bipy)( η -C 7 H 7 )][PF 6 ] have been isolated. E ° values for the complexes [MoX(N–N)( η -C 7 H 7 )] z + , demonstrate that in each case the bipy derivative is more easily oxidised than the corresponding Bu t -dab analogue.

Synthesis and spectra of bis(tertiaryphosphine) derivatives of cycloheptatrienyltungsten complexes

Abstract Reaction of [WI(CO) 2 (η 7 -C 7 H 7 )] with dppm (dppm = Ph 2 PCH 2 PPh 2 ) or dppe (dppe = Ph 2 PCH 2 CH 2 PPh 2 ) gives the trihaptocycloheptatrienyl complexes [WI(CO) 2 (L-L)(η 3 -C 7 H 7 )] [L-L = dppm, ( A 1 ); L-L = dppe ( A 2 )]. The complex A 1 reacts with NH 4 PF 6 to give the unidentate biphosphine complex [W(CO) 2 (dppm-P)(η 7 -C 7 H 7 )][PF 6 ] ( B ) which yields [W(CO)(dppm)(η 7 -C 7 H 7 )][PF 6 ] ( C ) on reaction with Me 3 NO·2H 2 O. Substitution of a carbonyl ligand in [W(CO) 3 (η 7 -C 7 H 7 )][PF 6 ] with the organometallic phosphine ligand [Mo(CO) 2 (dppe-P)(η 7 -C 7 H 7 )][PF 6 ] yields the heterobimetallic [{W(CO) 2 (η 7 -C 7 H 7 )}(μ-dppe){Mo(CO) 2 (η 7 -C 7 H 7 )}x][PF 6 ] 2 ( D ).

Synthesis and X-ray crystal structures of the cyclic oxacarbene complexes (n = 1 or 2): boat conformation of the 2-oxacyclohexylidene ligand

Abstract The cyclic oxacarbene complexes (dppe = Ph2 PCH2CH2PPh2; n = 1, 1 or 2, 2 ) have been synthesised by reaction of hydroxyalk-1-ynes, HCC(CH2)nCH2OH with [RuCl(dppe)(ν−C5H5)]/NH4[PF6] in refluxing methanol. The X-ray crystal structures of 1 and 2 reveal essentially vertically orientated carbene ligands with the oxygen directed ‘down’ away from the cyclopentadienyl ring. Both carbene rings exhibit folded conformations; the five-membered ring of 1 adopts an envelope configuration whilst the six-membered ring of 2 has a boat conformation.