No abstract

Chitosan has been explored as a potential component of biomaterials and scaffolds for many tissue engineering applications. Hybrid materials, where organic and inorganic networks interpenetrate at the molecular level, have been a particular focus of interest using 3-glycidoxypropyl trimethoxysilane (GPTMS) as a covalent crosslinker between the networks in a sol-gel process. GPTMS contains both an epoxide ring that can undergo a ring opening reaction with the primary amine of chitosan and a trimethoxysilane group that can co-condense with silica precursors to form a silica network. While many researchers have exploited this ring-opening reaction, it is not yet fully understood and thus the final product is still a matter of some dispute. Here, a detailed study of the reaction of GPTMS with chitosan under different pH conditions was carried out using a combination of solution state and solid state MAS NMR techniques. The reaction of GPTMS with chitosan at the primary amine to form a secondary amine was confirmed and the rate was found to increase at lower pH. However, a side-reaction was identified between GPTMS and water producing a diol species. The relative amounts of diol and chitosan-GPTMS species were 80 and 20% respectively and this ratio did not vary with pH. The functionalisation pH had an effect on the mechanical properties of 65 wt% organic monoliths where the properties of the organic component became more dominant. Scaffolds were fabricated by freeze drying and had pore diameters in excess of 140 mm, and tailorable by altering freezing temperature, which were suitable for tissue engineering applications. In both monoliths and scaffolds, increasing the organic content disrupted the inorganic network, leading to an increase in silica dissolution in SBF. However, the dissolution of silica and chitosan was congruent up to 4 weeks in SBF, illustrating the true hybrid nature resulting from covalent bonding between the networks.

The synthesis of the first trinuclear carbonyl clusters containing ligands derived from di(2-pyridyl)amine (Hdpa) has been achieved. Treatment of [Ru3(CO)12] or [Ru3(CO)10(MeCN)2] with di(2-pyridyl)amine (Hdpa) gives the cluster complex [Ru3(μ-Η)(μ-η3-dpa-C,N,N)(CO)9] (1). The dpa ligand in this compound chelates a Ru atom through both pyridinic nitrogens while attached to another Ru atom through the C atom of a metalated pyridine ring, keeping the amino NH fragment uncoordinated. Curiously, the osmium compounds [Os3(μ-Η)(μ-η2-dpa-N,N)(CO)10] (2) and [Os3(μ-Η)(μ3-η2-dpa-N,N)(CO)9] (3), which have been stepwise prepared from [Os3(CO)10(MeCN)2] and Hdpa, contain edge-bridging (2) and face-capping (3) N-deprotonated dpa ligands coordinated through the N atom of a pyridine ring and the N atom of the original amino fragment.

No abstract

The compound [Ru3(mu-H)(mu3-eta2-ampy)(CO)9] (1; Hampy =2-amino-6-methylpyridine) reacts with diynes RC4R in THF at reflux temperature to give the ynenyl derivatives [Ru3(mu3-eta2-ampy)(mu-eta3-RC...CC-CHR)(mu-CO)2-(CO)6] (2: R=CH2OPh; 3: R=Ph). These products contain a 1,4-disubstituted butynen-3-yl ligand attached to two ruthenium atoms. The compound [Ru3(mu-eta2-ampy)[mu3-eta6-PhCC5(C...CPh)-HPh2](CO)7] (4), which contains an eta5-cyclopentadienyl ring and a bridging carbene fragment, has also been obtained from the reaction of 1 with diphenylbutadiyne. This compound arises from a remarkable [3+2] cycloaddition reaction of a preformed 1,4-diphenylbutynen-4-yl ligand with a triple bond of a second diphenylbutadiyne molecule. The reactivity of the ynenyl derivatives 2 and 3 with diynes and alkynes has been studied. In all cases, compounds of the general formula [Ru3(mu-eta2-ampy)[mu3-eta5-C(=CHR)C=CRCR1=CR2](CO)7] (5-17) have been obtained. They all contain a ruthenacyclopentadienyl fragment formed by coupling of the coordinated ynenyl ligand of 2 (R = CH2OPh) or 3 (R = Ph) with a triple bond of the new reagent (the CR1=CR2 fragment results from the incoming diyne or alkyne reagent). While most of the products derived from 2 have the alkenyl C=CHR fragment with a Z configuration (R cis to Ru), all the compounds obtained from 3 have this fragment with an E configuration. Except 2 and 3, all the cluster complexes described in this article have a five-electron donor ampy ligand attached to only two metal atoms, a coordination mode unprecedented in cluster chemistry.

No abstract

Cationic palladium(II) complexes containing the chiral N-heterocyclic carbene (NHC) ligand 1-ethylenethiolate-3-methyl-4-(R)-phenylimidazoline-2-ylidene haVe been prepared in one-pot reactions that inVolVe the oxidatiVe addition of the C-S bond of methyl leVamisolium to [Pd(dba) 2 ] (dba ) dibenzylidene acetone). These reactions represent an easy entry into complexes haVing chiral NHC ligands.

No abstract