Formation of Ethers from Alcohols with Chloride Complexes of Platinum(II) as Catalysts

A new catalytic reaction of the etherification of alcohols in the system ROH-PtCl ₄ ²⁻ has been observed. At 70 °C in the presence of catalytic amounts of chloride complexes of platinum(II) methanol gave dimethyl ether. Methyl tert-butyl ether and di-tert-butyl ether were formed analogously from a mixture of methanol and tert-butanol. In the reaction with ethanol the products were diethyl ether and a π-ethylene complex of platinum(II). It is suggested that the step-wise mechanism includes the oxidative addition of the alcohol with the intermediate formation of an alkyl complex of platinum(IV), the decomposition of which by reductive elimination under the influence of a second molecule of alcohol or an alkoxide anion gives an ether and regenerates the catalyst, a chloride complex of platinum(II).__________Translated from Teoreticheskaya i Eksperimental’naya Khimiya, Vol. 41, No. 3, pp. 190–193, May–June, 2005.     

Conversion of trans‐Diboran(4)yl Platinum Complexes into Their cis‐Bisboryl Analogues

The diboran(4)yl trans‐[(iPr₃P)₂Pt(Br){B(NMe₂)B(NMe₂)Br}] ( 1 ) is readily converted into its cis‐bisboryl analogues 2 and 3 by reaction with the chelating bisphosphines 1,2‐bis(dicyclohexylphosphino)ethane (dcpe) and 1,1‐bis(dicyclohexylphosphino)methane (dcpm), respectively. A plausible mechanism of this transformation consists of a sequence of reductive diborane(4) elimination and subsequent reoxidative addition of its B? B bond to the low‐valent platinum centers. Thus, the forced cis configuration of the phosphine ligands induces a change in the preferred reaction site of the diborane(4) with respect to oxidative addition. The reactions proceed with high selectivities, and the cis‐bisboryl complexes 2 and 3 were isolated in moderate yields (55 and 46 %). Moreover, their identity was clearly verified by NMR spectroscopy and X‐ray diffraction studies.     

Platinum trans‐Bis(borirene) Complexes Displaying Coplanarity and Communication Across a Platinum Metal Center

Ambient‐temperature photolysis of the aminoborylene complex [(OC)₅Cr?B?N(SiMe₃)₂] in the presence of a series of trans‐bis(alkynyl)platinum(II) precursors of the type trans‐[Pt(CCAr)₂(PEt₃)₂] (Ar=Ph, p‐C₆H₄OMe, and p‐C₆H₄CF₃) successfully leads to twofold transfer of the borylene moiety [ : B?N(SiMe₃)₂] onto the alkyne functionalities. The alkynyl precursors and resultant bis(borirene)platinum(II) complexes formed are of the type trans‐[Pt(B{?N(SiMe₃)₂}C?CAr)₂(PEt₃)₂] (Ar=Ph, p‐C₆H₄OMe, and p‐C₆H₄CF₃). These species have all been successfully characterized by NMR, IR, and UV/Vis spectroscopy as well as by elemental analysis. Single‐crystal X‐ray diffraction has verified that these trans‐bis(borirene)platinum(II) complexes display coplanarity between the twin three‐membered rings across the platinum core in the solid state and stand as the first examples of coplanar conformations of twin borirene systems. These complexes were modeled using density functional theory (DFT), providing information helpful in determining the ability of the transition metal core to interact with each individual borirene ring system and allowing for the observed coplanarity of these rings in the solid state. This proposed transition metal interaction with the twin borirene systems is manifested in the electronic characterization of these borirene species, which display divergent photophysical UV/Vis spectroscopic profiles compared to a previously published mono(borirene)platinum(II) complex.     

A B–C Double Bond Unit Coordinated to Platinum: An Alkylideneboryl Ligand that Is Isoelectronic to Neutral Aminoborylene Ligands

The reaction of [Pt(PCy₃)₂] with Br₂B‐CH(SiMe₃)₂ resulted in generation of the first alkylideneboryl complex, trans‐[Br(Cy₃P)₂Pt{B?CH(SiMe₃)}], with concomitant elimination of Me₃SiBr. The trans bromide ligand of the alkylideneboryl complex was readily substituted by a methyl group upon treatment with methyllithium, leading to another alkylideneboryl complex, trans‐[Me(Cy₃P)₂Pt{B?CH(SiMe₃)}]. Various spectrochemical techniques, single‐crystal X‐ray crystallography, and quantum chemical calculations confirmed the formulation of a double bond between the boron and the carbon atom. The theoretical studies also provided evidence for the stronger trans influence of the alkylideneboryl ligand over iminoboryl and oxoboryl ligands.     

4-(4-甲基苯基)-6-苯基-2,2′-二联吡啶芳炔铂(II)络合物的合成及光物理性质

设计合成以4-甲基苯基-6-苯基-2,2′-二联吡啶为主配体、芳炔为辅助配体的铂(II)络合物1-3.与苯乙炔、萘乙炔为辅助配体的络合物1,2相比,蒽乙炔4-(4-甲基苯基)-6-苯基-2,2′-二联吡啶铂(II)络合物MLCT激发态的能量升高.     

Experimental studies on the trans-influence of boryl ligands in square-planar platinum(II) complexes

A series of platinum(II) boryl complexes of general formula trans-[(Cy(3)P)2Pt(Br)(BX2)], including the rare dibromoboryl species trans-[(Cy(3)P)2Pt(Br)(BBr2)], were synthesized by oxidative addition of the B-Br bond of a number of bromoboranes to [Pt(PCy3)2]. X-ray diffraction studies were performed on several such compounds. Comparison of the Pt--Br bond lengths allowed an empirical assessment of the trans-influence of different boryl ligands. A trans-influence scale was thus deduced and the results were compared with those previously computed for compounds of the type trans-[(Me(3)P)2Pt(Cl)(BX2)].     

Correlations and Contrasts in Homo‐ and Heteroleptic Cyclic (Alkyl)(amino)carbene‐Containing Pt0 Complexes

An improved synthetic route to homoleptic complex [Pt(CAAC^Me)₂] (CAAC=cyclic (alkyl)(amino)carbenes) and convenient routes to new heteroleptic complexes of the form [Pt(CAAC^Me)(PR₃)] are presented. Although the homoleptic complex was found to be inert to many reagents, oxidative addition and metal‐only Lewis pair (MOLP) formation was observed from one of the heteroleptic complexes. The spectroscopic, structural, and electrochemical properties of the zero‐valent complexes were explored in concert with density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) calculations. The homoleptic [Pt(CAAC)₂] and heteroleptic [Pt(CAAC)(PR₃)] complexes were found to be similar in their spectroscopic and structural properties, but their electrochemical behavior and reactivity differ greatly. The unusually strong color of the CAAC‐containing Pt⁰ complexes was investigated by TD‐DFT calculations and attributed to excitations into the LUMOs of the complexes, which are predominantly composed of bonding π interactions between Pt and the CAAC carbon atoms.     

Bioactive Platinum(IV) Complexes Incorporating Halogenated Phenylacetates

A new series of cytotoxic platinum(IV) complexes (1–8) incorporating halogenated phenylacetic acid derivatives (4-chlorophenylacetic acid, 4-fluorophenylacetic acid, 4-bromophenylacetic acid and 4-iodophenylacetic acid) were synthesised and characterised using spectroscopic and spectrometric techniques. Complexes 1–8 were assessed on a panel of cell lines including HT29 colon, U87 glioblastoma, MCF-7 breast, A2780 ovarian, H460 lung, A431 skin, Du145 prostate, BE2-C neuroblastoma, SJ-G2 glioblastoma, MIA pancreas, the ADDP-resistant ovarian variant, and the non-tumour-derived MCF10A breast line. The in vitro cytotoxicity results confirmed the superior biological activity of the studied complexes, especially those containing 4-fluorophenylacetic acid and 4-bromophenylacetic acid ligands, namely 4 and 6, eliciting an average GI₅₀ value of 20 nM over the range of cell lines tested. In the Du145 prostate cell line, 4 exhibited the highest degree of potency amongst the derivatives, displaying a GI₅₀ value of 0.7 nM, which makes it 1700-fold more potent than cisplatin (1200 nM) and nearly 7-fold more potent than our lead complex, 56MESS (4.6 nM) in this cell line. Notably, in the ADDP-resistant ovarian variant cell line, 4 (6 nM) was found to be almost 4700-fold more potent than cisplatin. Reduction reaction experiments were also undertaken, along with studies aimed at determining the complexes’ solubility, stability, lipophilicity, and reactive oxygen species production.     

Platinum complexes of naphthalene-1,8-dichalcogen and related polyaromatic hydrocarbon ligands

Platinum bisphosphine complexes bearing dichalcogen-derivatised naphthalene, acenaphthene or phenanthrene ligands have been prepared by either oxidative addition to zero-valent platinum species or from [PtCl(2)(PPhR(2))] (R=Ph or Me) and the disodium or dilithium salts of the parent disulfur, diselenide or mixed S/Se species. The parent naphthalene, acenaphthene and phenanthrene chalcogen compounds were treated with either [Pt(PPh(3))(4)] or [Pt(C(2)H(4))(PMe(3))(2)] (prepared in situ from [PtCl(2)(PMe(3))(2)], ethene and sodium naphthalide or super hydride [LiBEt(3)H]) to give the appropriate platinum(II) species. The dilithium salts of 1,8-E(2)-naphthalene (E=S or Se) prepared in situ by reduction of the E-E bond with [LiBEt(3)H] were treated with [PtCl(2)(PPh(3))(2)] to give [Pt(1,8-E(2)-nap)(PPh(3))(2)]. The tetraoxides [Pt(1,8-(S(O)(2))(2)-nap)(PR(3))(2)] (PR(3)=PPh(3) or PMe(2)Ph) were prepared in a similar metathetical manner from the appropriate [PtCl(2)(PR(3))] complexes and the disodium salt of naphthalene 1,8-disulfinic acid (1,8-(S(O)ONa)(2)-nap). The X-ray structures of selected examples reveal bidentate coordination with the naphthalene-E(2) unit hinged (111-137 degrees) with respect to the coordination plane. The naphthalene ring suffers significant distortion from planarity.     

Bis‐NHC Chelate Complexes of Nickel(0) and Platinum(0)

For a long time d¹⁰‐ML₂ fragments have been known for their potential to activate unreactive bonds by oxidative addition. In the development of more active species, two approaches have proven successful: the use of strong σ‐donating ligands leading to electron‐rich metal centers and the employment of chelating ligands resulting in a bent coordination geometry. Combining these two strategies, we synthesized bis‐NHC chelate complexes of nickel(0) and platinum(0). Bis(1,5‐cyclooctadiene)nickel(0) and ‐platinum(0) react with bisimidazolium salts, deprotonated in situ at room temperature, to yield tetrahedral or trigonal‐planar bis‐NHC chelate olefin complexes. The synthesis and characterization of these complexes as well as a first example of C? C bond activation with these systems are reported. Due to the enforced cis arrangement of two NHCs, these compounds should open interesting perspectives for bond‐activation chemistry and catalysis.     

Isolation and Characterization of Crystalline,Neutral Diborane(4) Radicals

Diaryldihalodiboranes(4) were reacted with bis(amidinato)‐ and bis(guanidinato)silylenes to generate the first neutral diborane‐centered radicals. These formally non‐aromatic 5π electron systems are stable in the solid state as well as in solution and were characterized by solid‐state structure determination, high‐resolution mass spectrometry, and EPR spectroscopy. The reactivity of one of these radicals with the oxidant 1,4‐benzoquinone led to ring‐opening and B?O bond formation.     

Induction of Immunogenic Cell Death by Chemotherapeutic Platinum Complexes

There is compelling evidence suggesting that the immune‐modulating effects of many conventional chemotherapeutics, including platinum‐based agents, play a crucial role in achieving clinical response. One way in which chemotherapeutics can engage a tumor‐specific immune response is by triggering an immunogenic mode of tumor cell death (ICD), which then acts as an “anticancer vaccine”. In spite of being a mainstay of chemotherapy, there has not been a systematic attempt to screen both existing and upcoming Pt agents for their ICD ability. A library of chemotherapeutically active Pt agents was evaluated in an in vitro phagocytosis assay, and no correlation between cytotoxicity and phagocytosis was observed. A Pt^II N‐heterocyclic carbene complex was found to display the characteristic hallmarks of a type II ICD inducer, namely focused oxidative endoplasmic reticulum (ER) stress, calreticulin exposure, and both HMGB1 and ATP release, and thus identified as the first small‐molecule immuno‐chemotherapeutic agent.     

Diborane(4) Azides: Surprisingly Stable Sources of Transient Iminoboranes

Herein we describe the first examples of isolable electron‐precise diboranes(4) that bear azide moieties: the acyclic 1,2‐diazido‐1,2‐bis(dimethylamino)diborane(4) and the cyclic 1,4‐diaryl‐2,3‐diazido‐1,4‐diaza‐2,3‐diborinines (aryl=mesityl, 2,6‐xylyl, 4‐tolyl). The reported examples are not only stable enough to be observed and isolated (putative transient diborane(4) azides previously reported by our group spontaneously decompose even below room temperature), but some of them are even robust enough to undergo controlled pyrolysis without explosive decomposition at temperatures well above 100 °C. In two cases, the controlled pyrolysis allows the isolation of complex diazaboretidines, which are the apparent dimerization products of endocyclic boryl‐iminoboranes.     

1-β-D-呋喃核糖基-1,2,4-三唑-3-酰胺铂配合物的合成研究

cis-[Pt(DMSO)₂Cl₂], K[Pt(DMSO)Cl₃]分别与两摩尔1-β-D-呋喃核糖基-1,2,4-三唑-3-酰胺(Ribavirin)进行络合反应, 制得了高收率的二配位铂配合物; 讨论了不同摩尔的1-β-D-呋喃核糖基-1,2,4-三唑-3-酰胺与cis-[Pt(DMSO)₂Cl₂]和K[Pt(DMSO)Cl₃]进行络合反应的结果; 对[Pt (N⁴,N⁷-Ribavirin)(DMSO)Cl]配合物(1)的X衍射晶体结构进行了测定.