Augusto Tassan

Synthesis, coordination and reactivity of 2-(trimethylsiloxymethyl)phenyl- and 2-(hydroxymethyl)phenyl isocyanides

Abstract 2-(Trimethylsiloxymethyl)phenyl isocyanide, 2-(CH 2 OSiMe 3 )C 6 H 4 NC ( 2 ) was prepared by reaction of 2-(trimethylsiloxymethyl)phenyl formamide, 2-(CH 2 OSiMe 3 )C 6 H 4 NHCHO ( 1 ) with trichloromethyl chloroformate. Reaction of 2 with F − ions in MeOH leads to the formation of 2-(hydroxymethyl)phenyl isocyanide, 2-(CH 2 OH)C 6 H 4 NC ( 3 ), which is stable as free ligand and does not spontaneously undergo intramolecular cyclization to 4H-benzo[1,3]oxazine. The isocyanide 2 coordinates to Pt(II) and Pd(II) metal ions such as in the complexes cis -[MCl 2 (CNC 6 H 4 2-CH 2 OSiMe 3 ) 2 ] and cis -[PdCl 2 (CNC 6 H 4 -2-CH 2 OSiMe 3 )(PPh 3 )], which are converted to the corresponding benzoxazin-2-ylidene derivatives [ MCl 2 ( CN ( H ) C 6 H 4 2- CH 2 O ) 2 ] and [ PdCl 2 ( CN ( H ) C 6 H 4 2- CH 2 O )( PPh 3 )] , respectively, in the presence of a catalytic amount of F − ions in MeOH. On the other hand, coordination of 2 to the {M(CO) 5 } (M=W, Cr) fragments and subsequent reactions with of F − ions in MeOH affords the corresponding 2-(hydroxymethyl)phenyl isocyanide complexes [M(CO) 5 (CNC 6 H 4 2-CH 2 OH)], where the hydroxy function does not react with the coordinated isocyanide group.

Transition metal coordination and reactivity of 2-(azidomethyl)-, 2-(chloromethyl)- and 2-(iodomethyl)phenyl isocyanides

Abstract 2-(Azidomethyl)phenyl isocyanide, 2-(CH 2 N 3 )C 6 H 4 NC (AziNC), coordinates to {M(CO) 5 } (M=W, Cr) fragments to afford the corresponding isocyanide complexes [M(CO) 5 (AziNC)] (M=W ( 1 ), Cr ( 2 )). AziNC coordinates also to some Au(I) species such as [AuCl(AziNC)] ( 3 ), derived from the reaction of [AuCl(Me 2 S)] with AziNC, and [Au(AziNC) 2 ][BF 4 ] ( 4 ), obtained from the reaction of 3 with AgBF 4 , followed by treatment with AziNC. Complexes 1 and 2 undergo the Staudinger reaction with PPh 3 affording the phosphinimine-isocyanide derivatives [M(CO) 5 {CNC 6 H 4 -2-(CH 2 NPPh 3 )}] (M=W ( 5 ), Cr ( 6 )). Complex 6 reacts with H 2 O affording a mixture of the amino–isocyanide [Cr(CO) 5 {CNC 6 H 4 -2-(CH 2 NH 2 )}] ( 7 ) and the carbene [Cr(CO) 5 { CN(H)C 6 H 4 -2-CH 2 N (H)}] ( 8 ) species. Complexes 3 and 4 react with 1 or 2 equiv. of PPh 3 displacing the isocyanide with the formation of the complexes [AuCl(PPh 3 )] ( 9 ) and [Au(PPh 3 ) 2 ][BF 4 ] ( 10 ), respectively. The halogeno–isocyanide complexes [W(CO) 5 (CNC 6 H 4 -2-CH 2 Cl)] ( 11 ) and [W(CO) 5 (CNC 6 H 4 -2-CH 2 I)] ( 12 ) show different reactivity towards amines so that only 12 reacts with MeNH 2 to afford in low yield the N -heterocyclic carbene species [W(CO) 5 { CN(H)C 6 H 4 -2-CH 2 N (Me)}] ( 13 ).

Oxidative addition of iodo-acetonitrile and of elemental halogens to [Pt3(µ-CO)3(PCy3)3]

The reaction of [Pt3(mu-CO)3(PCy3)3](1) with one mole-equivalent of iodo-acetonitrile was quantitative at -70 degrees C giving the oxidative addition product [Pt3(mu-CO)3(PCy3)3(I)(CH2CN)](2). Fragmentation of was observed in solution giving [Pt2I(CH2CN)(CO)2(PCy3)2](3) which is the major product at room temperature if the starting cluster/reactant ratio is equal to or less than 1 to 1.5. Dimer 3 decomposes slowly in solution giving [Pt2I2(CO)2(PCy3)2](4a) and succinonitrile. Monomer [PtI(CH2CN)(CO)(PCy3)] was the final product of the reaction when using excess of iodo-acetonitrile. The reactions of with one mole-equivalent of halogens X2 gave the new 44-electron clusters [Pt3X(micro-CO)2(micro-X)(PCy3)3](X = I2(7a) or Br2(7b)) by oxidative addition followed by substitution of CO by X-. Fragmentation of and took place in solution when using one and a half mole-equivalents of X2 giving dimers 4a and [Pt2Br2(CO)2(PCy3)2](4b) as well as [Pt2X2(mu-X)2(CO)2(PCy3)2]. Monomers cis-[PtX2(CO)(PCy3)] were the final products of the reaction of with excess of halogens. Insertion of SnCl2 was observed into the Pt-Pt bond but not into the Pt-X bond, when equimolar amounts of SnCl2 x 2H2O were added to a solution of 4a or its chloro-analogue giving [Pt2X2(micro-SnCl2)(CO)2(PCy3)2]. The Pt(I) dimers have unusually small J(Pt-Pt) values as observed by 195Pt NMR and calculated by DFT. These values showed periodic changes comparing 4a and its analogues with other halides and mixed halide dimers.

Synthesis and transition metal coordination of 2-(azidomethyl) phenyl isocyanide

Abstract The reaction of 2-(chloromethyl)phenyl formamide, 2-(CH2Cl)C6H4NHCHO, with NaN3 in DMSO at room temperature affords 2-(azidomethyl)phenyl formamide, 2-(CH2N3)C6H4NHCHO (1), which is then dehydrated to 2-(azidomethyl)phenyl isocyanide, 2-(CH2N3)C6H4NC, (2) upon reaction with SOCl2 in DMF at low temperature. The coordination ability of the isocyanide 2 has been tested towards some Pt(II), Pd(II) and W(0) metal complexes to yield derivatives of the type [PtCl2(CNC6H4-2-CH2N3)2], [PdCl2(CNC6H4-2-CH2N3)(PPh3)] and [W(CO)5(CNC6H4-2-CH2N3)], respectively.

Synthesis, characterization and cytotoxic activity of substituted benzyl iminoether Pt(II) complexes of the type cis- and trans-[PtCl2{E-N(H)=C(OMe)CH2-C6H4-p-R}2] (R=Me, OMe, F). X-ray structure of trans-[PtCl2{E-N(H)=C(OMe)CH2-C6H4-p-F}2].

New substituted benzyl iminoether derivatives of the type cis- and trans-[PtCl(2){E-N(H)C(OMe)CH(2)-C(6)H(4)-p-R}(2)] (R=Me (1a, 2a), OMe (3a, 4a), F (5a, 6a)) have been synthesized and characterized by elemental analyses, FT-IR spectroscopy and NMR techniques. The iminoether ligands are in the E configuration, which is stable in solution and in the solid state, as confirmed by the (1)H NMR data. Complex trans-[PtCl(2){E-N(H)C(OMe)CH(2)-C(6)H(4)-p-F}(2)] (6a) was also characterized by an X-ray diffraction study. Complexes 1a-6a have been tested against a panel of human tumor cell lines in order to evaluate their cytotoxic activity. cis-Isomers were significant more potent than the corresponding trans-isomers against all tumor cell lines tested; moreover, complexes 1a and 5a showed IC(50) values from about 2-fold to 6-fold lower than those exhibited by cisplatin, used as reference platinum anticancer drug.

Reaction of triangulo-clusters [Pt3(μ-CO)3(PR3)3] with hexafluorobutyne. The X-ray crystal structures of [Pt2(CO)2(PR3)2(μ-η2:η2-CF3CCCF3)](PR3= PPh3 or PCy3) and [Pt2(CO)2(PBzPh2)(μ-η1:η1-CF3CCCF3)2]

Hexafluoro-2-butyne, CF3CCCF3, reacts with the triangulo-clusters [Pt3(μ-CO)3(PR3)3] to give the diplatinum(0) compounds [Pt2(CO)2(PR3)2(μ-η2:η2-CF3CCCF3)] {PR3 = PPh3 (1), PBzPh2 (2), PCy3 (3), PiPr3 (4)}. Spectroscopic properties are reported which are in accord with the molecular structures for 1 and 3, both having the acetylenic C–C axis perpendicular to the Pt–Pt axis, bridging two [Pt(CO)(PR3)] fragments in a μ-η2:η2 fashion. A large excess of hexafluorobutyne slowly converts 1 and 2 to the diplatinum(II) complexes [Pt2(CO)2(PR3)2(μ-η1:η1-CF3CCCF3)2] {PR3 = PPh3 (5), PBzPh2 (6)}, having two planar hexafluorobutyne bridges. This stereochemistry has been established by NMR and IR spectra, and confirmed by single-crystal X-ray diffraction.

The Reaction of Alkenes with Triangulo-Clusters [Pt3(μ-CO)3(PR3)3]

The reactions of the cluster complexes [Pt3(μ-CO)3L3], where L=PPh3 1a, PPh2Bz 1b and PCy3 1c, with activated mono-olefins have been studied under preparative and equilibrium conditions. At low temperature the olefins react quantitatively giving the adducts [Pt3(μ-CO)3L3(olefin)] (olefin=trans-dicyanoethene, DCE 2a–2c, maleic anhydride, MA 3a–3c). The stereo-chemistry of these unstable clusters has been deduced from low temperature 31P, 13C, 195Pt-NMR and I.R. spectra. At higher temperature these adducts in presence of excess of olefin convert quantitatively to stable mononuclear Pt(0) complexes [Pt(CO)L(olefin)] (olefin=DCE 4a–4c, MA 5a–5c, maleimide, MI 6a–6c and 1–4-naphthoquinone, NQ 7a, 7c).

A FACILE ENRICHMENT IN 13CO OF TETRAIRIDIUM CARBONYL CLUSTER COMPOUNDS PROMOTED BY TRIMETHYLAMINE OXIDE

Abstract The reactions of anionic clusters [Ir 4 (CO) 11 X] − (X=Br, I), with excess of 13 CO gave enriched Ir 4 ( * CO) 12 ; the level of 13 CO enrichment was 9.2%, corresponding to stoichiometric replacement of the labile ligand X − . From the enriched Ir 4 ( * CO) 12 the equi-enriched derivatives [Ir 4 ( * CO) 11 X] − can be prepared, on which the exchange of X − with 13 CO can be carried out again. This 12 CO–(X − )– 13 CO exchange cycle can be repeated until required. An alternative process for more profitable and general enrichment of Ir 4 (CO) 12 derivatives involves replacement of coordinated 12 CO by free 13 CO promoted by Me 3 NO, which acts as an oxidative decarbonylating reagent.

Efficient Microscale Preparation of Isotopically Enriched 1‐[79Br]Bromo‐2‐Fluoroethylene, [79Br]BrHC˭CHF

Abstract An efficient preparation of 1‐[79Br]bromo‐2‐fluoroethylene, [79Br]BrHC˭CHF, was carried out by a three‐step procedure: (a) natural 1‐bromo‐2‐fluoroethylene, BrHC˭CHF, was iodinated to 1‐fluoro‐2‐iodoethylene, FHC˭CHI; (b) 1‐fluoro‐2‐iodoethylene was 79Br2‐brominated to 1,2‐di[79Br]bromo‐1‐fluoro‐2‐iodoethane, [79Br]BrFCHCH[79Br]BrI; and (c) 1,2‐di[79Br]bromo‐1‐fluoro‐2‐iodoethane was dehalogenated to 1‐[79Br]bromo‐2‐fluoroethylene, [79Br]BrHC˭CHF. The yield of isolated product, on a 2‐mmol scale, was 62% with respect to 79Br2.

Comparative neutron and X-ray study of [PPN][HIr4(CO)9(μ-Ph2PCH2PPh2)]

Abstract The structure of this tetranuclear iridium cluster featuring a terminal Ir–H bond has been investigated by neutron crystallography using the D19 diffractometer at the Institut Laue Langevin in Grenoble. The structure, which is stabilized by numerous C–H⋯O=C hydrogen bonds, has no π–π stacking. The neutron study described here resolves a difficulty encountered in previous X-ray work where it proved impossible to locate reliably the position of hydrogen in the presence of heavy iridium atoms. Neutron crystallography offers unique advantages for this type of problem and in this case has provided the first reliable value for a terminal Ir–H distance of 1.618(14) Å and an intramolecular H–H contact of 2.40(2) Å.