Christopher Crocker

Rapid reversible fission of a C–H bond in a metal complex: X-ray crystal structure of [RhHCl(But2PCH2CH2CHCH2CH2PBut2)]

The occurrence and stereochemistry of a rapid reversible C–H fission in [[graphic omitted]But2)] is established by n.m.r. spectroscopy, including triple resonance INDOR, and by X-ray crystallography.

Transition metal–carbon bonds. Part 52. Large ring and cyclometallated complexes formed from But2PCH2CH2CHRCH2CH2PBut2(R H or Me) and IrCl3, or [Ir2Cl4(cyclo-octene)4] : crystal structures of the cyclometallated hydride, [IrHCl(But2PCH2CH2CHCH2CH2PBut2)], and the carbene complex [IrCl(But2PCH2CH2CCH2CH2PBut2)]

Treatment of But2P(CH2)5PBut2, with iridium trichloride gives a mixture of the 16-atom ring dihydride [lr2H2Cl4{But2P(CH2)5PBut2}2], a co-ordinatively saturated cyclometallated hydride, [[graphic omitted]But2)])(1b), which is non-fluxional, and an unidentified complex. A better route to the cyclometallated hydride (1b) is to treat [Ir2Cl2(C8H14)4](C8H14= cyclo-octene) with the diphosphine. Complex (1b) takes up carbon monoxide to give the six-co-ordinate [[graphic omitted]But2)] and loses dihydrogen on heating [ca. 200 °C (15 mmHg)] to give the very dark carbene/ylide complex [[graphic omitted]But2)](3)/(4). This carbene/ylide complex takes up dihydrogen at 20 °C (1 atm) to give back (1b). The diphosphine But2PCH2CH2CHMeCH2CH2PBut2 reacts with IrCl3 to give the 16-atom ring chelate [Ir2H2Cl4(But2PCH2CH2CHMeCH2CH2 PBut2)2], no cyclometallated product being detected. However, the complex [[graphic omitted]But2)], can be prepared from [Ir2Cl2(C8H14)4] and the diphosphine. Hydrogen-1, 13C, and 31P n.m.r. and i.r. data are reported. The crystal structures of (1b) and of the carbene/ylide (3)/(4) have been determined. Cell dimensions are, for (1b), a= 1 231.8(3), b= 1 435.9(3), c= 1 485.4(3) pm, and β= 104.82(2)° and for (3)/(4), a= 1 232.6(3), b= 1 436.2(3), c= 1 480.7(3) pm, and β= 104.87(2)°. The structures are isomorphous, with space group P21/c and Z= 4.

Further studies on the interconversion of large ring and cyclometallated complexes of rhodium, with the diphosphines But2P(CH2)5PBut2 and But2PCH2CHCHCH2PBut2

Improved routes to the fluxional cyclometallated hydride [[graphic omitted]But2)] are reported. Treatment of this hydride with carbon monoxide and sodium tetraphenylborate in methanol gives the fluxional salt [[graphic omitted]But2)][Bph4], together with a small amount of the 16-atom ring complex, trans-[Rh2Cl2(CO)2{But2P(CH2)5PBut2)2], more readily prepared by treating [Rh2Cl2(CO)4] with the diphosphine. This 16-atom ring complex exists as two rotamers in solution at 25 °C. Although [[graphic omitted]But2)] gives [[graphic omitted]But2)] with sodium propan-2-oxide and carbon monoxide on the other hand the corresponding complex [[graphic omitted]But2)] on similar treatment gives a complex mixture (probably containing rotamers of large-ring chelates). Treatment of [[graphic omitted]But2)] with MeNC and sodium propan-2-oxide also gives mixtures, probably containing large-ring chelates. Treatment of [[graphic omitted]But2)] with MeNC or ButNC in the presence of sodium tetraphenylborate or ammonium hexafluorophosphate gives 16-atom ring chelate salts [Rh2(CNR)4{But2P(CH2)5PBut2}2][anion]2 which can also be made by treating [Rh(CNR)4][anion] with the diphosphine. Rotation of trans-MeNC–Rh–CNMe moieties around P–Rh–P bonds has been studied by variable-temperature n.m.r. spectroscopy. The complex [Rh2(CNBut)4(But2PCH2CHCHCHCH2PBut2)2][PF6]2 has also been prepared. Treatment of the cyclooctene complex [Rh2Cl2(C8H14)4] with But2P(CH2)5PBut2 and MeNC or ButNC (1 mol per rhodium atom) gives 16-atom ring complexes of type [Rh2Cl2(CNR)2{But2P(CH2)5PBut2}2]. The complex [Rh2Cl2(CNMe)2{But2P(CH2)5PBut2}2] gives only one rotamer in solution in which the two rhodiums are chemically non-equivalent. The diphosphine But2PCH2CHCHCH2PBut2 reacts similarly with [Rh2Cl2(C8H14)4] and MeNC but also gives a small amount of another (unidentified) product. Infrared and 1H, 31P, and 103Rh n.m.r. data are given.

Transition metalcarbon bonds: LV. Cyclometallation and other reactions of PBut2Bui and PPh2Bui with platinum(II) and palladium(II)

Abstract The new phosphine, PBut2Bui (L), was prepared from But2PCl and LiBui. PPh2Bui (L′) was prepared from Ph2PCl and LiBui. Treatment of [PtCl2(NCBut)2] with L′ gives [PtCl2L′2] which does not cyclometallate even on prolonged boiling in 2-methoxyethanol. In contrast, [PtCl2(NCBut)2] reacts with PBut2Bui in boiling 2-methoxyethanol to give the cyclometallated complex [ Pt 2 Cl 2 (PBu t 2 CH 2 -CHMeCH 2)2] (II, X = Cl). The corresponding bromide, iodide and acetylacetonate were prepared. With PPh3 II (X = Cl) gives [ PtCl(PBu t 2 CH 2 CHMeCH 2)(PPh3)] which with NaBH4 gives [ PtH(PBu t 2 CH 2 CHMeC H2)(PPh3)]. Na2PdCl4 with L (2 mol equivalents) gave trans-[PdCl2L2], which was converted into trans-[Pd(NCS)2-L2] by metathesis with KSCN. Treatment of Na2PdCl4 with L (1 mol equivalent) gave [Pd2Cl4L2], which on heating in 2-methoxyethanol gave [ Pd 2 Cl 2 (PBu t 2 CH 2 -CHMeCH 2)2], as a mixture of syn- and anti-isomers. The complexes trans-[PdCl2-L′2] and [Pd2Cl4L′2] were also prepared. 1H- and 31P NMR data are given.

Transition metal–carbon bonds. Part 48. Allene complexes from halogeno-bridged platinum(II) complexes: crystal structures of cis-[PtCl2(PPrn3)(C3H4)] and cis-[PtCl2(PMe2Ph)(C3H4)]

A 31P n.m.r. study of the system [Pt2Cl4(PMe2Ph)2]–allene shows that at low temperatures (e.g. 213 K)trans-[PtCl2(PMe2Ph)(C3H4)] forms rapidly and reversibly. At 20 °C [Pt2Cl4(PR3)2](PR3= PPrn3, PMe2Et, or PMe2Ph) react with allene to give colourless complexes cis-[PtCl2(PR3)(C3H4)], the crystal structures of the PPrn3 and PMe2Ph complexes were determined by X-ray diffraction. Crystal data are for [PtCl2(PPrn3)(C3H4)]a= 15.461 (2), b= 11.437(2), c= 9.606(2)A, space group Pna21, with Z= 4 and for [PtCl2(PMe2Ph)(C3H4)]a= 8.398(2), b= 10.209(3), c= 15.677(4)A, space group P212121, and Z= 4. Final R factors are R= 0.026 and 0.029 respectively. These cis complexes dissociate very slowly in solution, in contrast with cis-[PtCl2(PPh3)-(C3H4)], which was previously reported to be unstable. Treatment of cis-[PtCl2(PMe2Ph)(C3H4)] with [Pt2Cl4-(PMe2Ph)2] gives what is probably the µ-allene complex cis,cis-[(PhMe2P)Cl2Pt(C3 H4) PtCl2(PMe2Ph)] which was too insoluble to characterize fully. Treatment of [NBun4]2[Pt2X6](X = Cl, Br, or I) with an excess of allene gives the salts [NBun4][PtX3(C3H4)]. Treatment of [NBun4][PtX3(C3H4)] with [NBun4]2[Pt2X6](X = Cl or Br) gave the µ-allene complexes [NBun4]2[X3Pt(C3H4)PtX3]. The NPrn4 salt was also made. Proton, 13C, and 31P n.m.r. data and i.r. data are given and discussed.

Interaction of [Pt2Cl4(PPrn3)2] with some simple organic molecules

The reversible fission of the chloro-bridged complex [Pt2Cl4(PPrn3)2] by carbon monoxide, ethylene, phenylacetylene, methanol, water, tetrahydrofuran, phenol, acetone, cyclopentanone, benzophenone, acetaldehyde, benzaldehyde, acrolein, chloral, chloral hydrate, and methyl acetate is investigated by low-temperature 31P n.m.r. spectroscopy.

Transition metal–carbon bonds. Part 51. Action of amines on buta-1,3-diene complexes of type cis,cis-[Pt2Cl4(PR3)2(µ-C4H6)] : crystal structures of [ Pt2Cl4(PMe2Ph)2(µ-C4H6)](meso isomer) and [(Et3P)ClPt(Me2NCH2CHCHCH2NMe2)PtCl(PEt3)](two trans-fused five-membered rings)

Treatment of chloro-bridged complexes [Pt2Cl4(PR3)2](PR3= PMe2Ph, PEt3, or PPrn3) with buta-1,3-diene over several days gives the µ-butadiene complexes cis,cis-[Pt2Cl4(PR3)2(µ-C4H6)]; such complexes have not previously been fully characterized. Buta-1,3-diene is prochiral and the product is shown to be the meso isomer for PR3= PMe2Ph, by X-ray crystallography. A low-temperature study in CDCl3 shows that at –30 °C buta-1,3- diene reacts rapidly and reversibly with [Pt2Cl4(PPrn3)2] to give trans-[PtCl2(PPrn3)(C4H6)]; a very small amount of cis-[PtCl2(PPrn3)(C4H6)], in which the butadiene is monodentate, was also probably formed. Treatment of [NBun4]2[Pt2X6] with buta-1,3-diene gave the µ-butadiene complexes [NBun4]2[Pt2X6(µ-C4H6)](X = Cl or Br). Treatment of [Pt2Cl4(PMe2Ph)2] with isoprene at –60 °C reversibly gives a new species, probably trans-[Pt2Cl2(PMe2Ph)(isoprene)], and at room temperature probably cis-[PtCl2(PMe2Ph)(isoprene)], although we could not separate this cis species from the bridged complex. Treatment of cis,cis-[Pt2Cl4(PMe2Ph)2(µ-C4H6)] with an excess of dimethylamine (even at –78 °C) rapidly gave [(PhMe2P)Cl[graphic omitted]tCl(PMe2Ph)](5a); a similar reaction gave the PEt3 complex (5d), the crystal structure of which shows the presence of two trans-fused five-membered rings. Treatment of cis,cis-[Pt2Cl4(PPrn3)2(µ-C4H6)] with methylamine similarly gave [(Prn3P)Cl[graphic omitted]tCl(PPrn3)] as a mixture of three isomers due to the positioning of the N–Me groups; one isomer was isolated pure. Proton, 13C, 31P, and 195Pt n.m.r. and i.r. data are given. Crystals of both the title compounds are monoclinic, space group P21/n, with Z= 2 and molecular symmetry Ci. Those of [Pt2Cl4(PMe2Ph)2(µ-C4H6)] have a= 1.9658(4), b= 0.9741(3), c= 0.6557(1) nm, and β= 94.24(2)°. Those of (5d) have a= 0.8015(3), b= 1.3461(3), c= 1.3070(3) nm, and β= 97.56(3)°. Final R factors were 0.042 for 1 391 and 0.040 for 1 584 observed reflections, respectively.

The interaction of vinyl acetate and allyl acetate with chloro-bridged platinum(II) complexes [Pt2Cl4(PR3)2]: Crystal structure of cis-[PtCl2(PMe2Ph2)(CH2=CHOCOCH3)]

Abstract Five complexes of type cis-[PtCl2(PR3)Q] (PR3 =PMe3, PMe2Ph, PEt3; Q = CH2 CHOCOCH3 or CH2=CHCH2OCOCH3) have been prepared. The crystal structure of cis-[PtCl2[PME2Ph)(CH2=CHOCOCH3)] is described. Crystals of cis-[PtCl2(PME2Ph)(CH2-CHOCOCH3)] are triclinic, with a 8.441(4), b 13.660(5), c 7.697(3) A, a 101.61(3)°, β 111.85(3)° γ 95.22(3)°, pP1, Z = 2. The structure was determined from 2011 reflections I σ 3σ (I) and refined to R = 0.037. The CH3COO grouping is syn to the cis-PMe2Ph ligand, with bond lengths of PtCl (trans to P) 2.367(3), PtCl (trans to olefin) 2.314(3), PtP 2.264(2), and PtC of 2.147(12) and 2.168(11) A. The complexes cis-[PtCl2- (PR3)Q] were studied by variable temperature 1H and 31P NMR spectroscopy. Spectra of the vinyl acetate complexes were temperature dependent as a result of rotation about the platinum—olefin bond. The rotation was “frozen out” at ca. 240 K; for cis-[PtCl2(PME2Ph)(CH2=CHOCOCH3] ΔG≠ (rotation) 15.0 ± 0.2 kcal mol-1. NMR parameters for the rotamers are reported. NMR studies of the interaction between chloro-bridged complexes of type [Pt2Cl2(PR3)2] (PR3 = P-N-Pr3 or PMe2Ph) and vinyl acetate shows that even at low temperatures (213 K) equilibrium favours the bridged complex and the proportion of trans-[PtCl2(PR3)CH2=CHOCOCH3)] is very small e.g. 2%. The allyl acetate complexes cis-[PtCl2(PR3)(CH2=CHCH2OCOCH3)] showed only one rotamer over the range 333–213 K. Reversible dissociation of cis-[PtCl2(PMe2Ph)- (CH2=CHCH2OCOCH3)] to [Pt2Cl4(PMe2Ph)2] + allyl acetate was studied at ambient temperature. At low temperatures e.g. 213–190 K addition of allyl acetate to a CDCl3 solution of [Pt2Cl2(P-n-Pr3)2] reversibly gave some olefin complex trans-[PtCl2(P-n-Pr3)(CH2=CHCH2OCOCH3)] and some O-bonded complex trans-[PtCl2(P-n-Pr3)(CH2=CHCH2OCOCH3)].

Direct oxidative addition–reductive elimination reactions between trans-[MCl(CO)L2] and [MCl3(CO)L2] or trans-[PtCl4(PEt3)2](M = Rh or Ir, L = tertiary phosphine)

Complexes of the type trans-[MCl(CO)L2] and [MCl3(CO)L2], M = Rh or Ir, L = PMe2Ph or PEt2Ph, have been shown to react with each other, presumably by a double chloro-bridged intermediate, and undergo rapid oxidative addition–reductive elimination; phosphine exchange is much slower. Similar results were obtained when trans-[PtCl4(PEt3)2] was treated with trans-[MCl(CO)(PEt3)2], M = Rh or Ir, for which rapid and complete conversion into trans-[PtCl2(PEt3)2] and [MCl3(CO)(PEt3)2] occurred. Phosphorus-31 n.m.r. data are given.

Transition metal–carbon bonds. Part 49. The action of amines on cis-[PtCl2(PPrn3)(C3H4)]: crystal structures of the complexes [PtCl(PPrn3){C(CH2)CH2NHBut}](four-membered ring) and [Pt2Cl2(PPrn3)2{C(CH2)CH2NHMe}2](eight-membered ring)

Addition of NR3(R = Me or Et) to the allene complex cis-[PtCl2(PPrn3)(C3H4)] rapidly gives the zwitterionic alkenyl complexes [PtCl2(PPrn3){C(CH2)CH2NR3}]. Addition of NH2But to the allene complex at or below –20° C gives an analogous complex, viz.[PtCl2(PPrn3){C(CH2)CH2NH2But}], but this with base, i.e. an excess of NH2But or preferably Na[OPri], immediately cyclizes to give [[graphic omitted]HBut}](5) the crystal structure of which has been determined and shown to contain a four-membered ring. Treatment of the allene complex with an excess of methylamine gives [[graphic omitted]HMe}2](6a) the crystal structure of which has also been determined and shown to contain an eight-membered ring. Benzylamine gives an analogous complex. Proton, 31P, and 195Pt n.m.r. data are given and discussed, as are i.r. data. Crystals of (5) are monoclinic, space group C2/c, with a= 19.653(3), b= 11.538(2), c= 18.785(2)A, β= 107.10(1)°, and Z= 8; R= 0.036 for 2 300 independent reflections. The complex (6a) is monoclinic, space group P21/n, with a= 11.315(3), b= 13.782(2), c= 11.385(3)A, β= 100.76(2)°, and Z= 2; R= 0.032 for 2 083 independent reflections.