Phosphido pincer complexes of platinum: synthesis, structure and reactivity

A series of platinum(II) complexes supported by the tridentate bis(phosphine)phosphido ligand bis(2-diisopropylphosphinophenyl)phosphide) [iPr–PPP] have been synthesized and characterized (1–4). X-Ray structural studies of [iPr–PPP]PtCl (1) and [iPr–PPP]PtCH3 (3) complexes show meridional [iPr–PPP] ligands around approximately square-planar platinum centers. Structural data and NMR analysis highlight a strong trans influence for the phosphido phosphorous donor, comparable to that of the anionic aryl carbon of the classic PCP pincer complexes. A series of thermally stable [PPP]Pt(IV) compounds, including [PPP]Pt(CH_3)_2X [X = I (5) and SbF_6 (6)], were also synthesized. The study of the binding affinity of SO_2 and NO to complex 1 has also been addressed

Mechanism of Isotactic Styrene Polymerization with a C6F5‑Substituted Bis(phenoxyimine) Titanium System

We report a combined, experimental and theoretical, study of styrene polymerization to clarify the regio- and stereocontrol mechanism operating with a C6F5-substituted bis(phenoxyimine) titanium dichloride complex. Styrene homopolymerization, styrene−propene and styrene− ethene−propene copolymerizations have been carried out to this aim. A combination of 13C NMR analysis of the chain-end groups and of the microstructure of the homopolymers and copolymers reveals that styrene polymerization is highly regioselective and occurs prevalently through 2,1- monomer insertion. DFT calculations evidenced that steric interaction between the growing chain and the monomer in the transition state insertion stage is at the origin of this selectivity. The formation of isotactic polystyrene with a chain-end like microstructure is rationalized on the base of a mechanism similar to that proposed for the syndiospecific propene polymerization catalyzed by bis(phenoxyimine) titanium dichloride complexes. Finally, a general stereocontrol mechanism operative in olefin polymerization with this class of complexes is proposed

Colorectal Cancer Stage at Diagnosis Before vs During the COVID-19 Pandemic in Italy

IMPORTANCE Delays in screening programs and the reluctance of patients to seek medical attention because of the outbreak of SARS-CoV-2 could be associated with the risk of more advanced colorectal cancers at diagnosis. OBJECTIVE To evaluate whether the SARS-CoV-2 pandemic was associated with more advanced oncologic stage and change in clinical presentation for patients with colorectal cancer. DESIGN, SETTING, AND PARTICIPANTS This retrospective, multicenter cohort study included all 17 938 adult patients who underwent surgery for colorectal cancer from March 1, 2020, to December 31, 2021 (pandemic period), and from January 1, 2018, to February 29, 2020 (prepandemic period), in 81 participating centers in Italy, including tertiary centers and community hospitals. Follow-up was 30 days from surgery. EXPOSURES Any type of surgical procedure for colorectal cancer, including explorative surgery, palliative procedures, and atypical or segmental resections. MAIN OUTCOMES AND MEASURES The primary outcome was advanced stage of colorectal cancer at diagnosis. Secondary outcomes were distant metastasis, T4 stage, aggressive biology (defined as cancer with at least 1 of the following characteristics: signet ring cells, mucinous tumor, budding, lymphovascular invasion, perineural invasion, and lymphangitis), stenotic lesion, emergency surgery, and palliative surgery. The independent association between the pandemic period and the outcomes was assessed using multivariate random-effects logistic regression, with hospital as the cluster variable. RESULTS A total of 17 938 patients (10 007 men [55.8%]; mean [SD] age, 70.6 [12.2] years) underwent surgery for colorectal cancer: 7796 (43.5%) during the pandemic period and 10 142 (56.5%) during the prepandemic period. Logistic regression indicated that the pandemic period was significantly associated with an increased rate of advanced-stage colorectal cancer (odds ratio [OR], 1.07; 95%CI, 1.01-1.13; P = .03), aggressive biology (OR, 1.32; 95%CI, 1.15-1.53; P < .001), and stenotic lesions (OR, 1.15; 95%CI, 1.01-1.31; P = .03). CONCLUSIONS AND RELEVANCE This cohort study suggests a significant association between the SARS-CoV-2 pandemic and the risk of a more advanced oncologic stage at diagnosis among patients undergoing surgery for colorectal cancer and might indicate a potential reduction of survival for these patients

Ring-Opening Polymerization of Cyclic Esters by Pincer Complexes Derived from Alkaline Earth Metals

We report the synthesis and characterization of new Ca(II) and Mg(II) complexes of the type [(Ph- PPP)MR] (M = Ca, R = N(SiMe3)2 (1); M = Mg, R = nBu (2)) where Ph-PPP is a tridentate monoanionic phosphido ligand (Ph-PPP-H =bis(2-diphenylphosphinophenyl)phosphine). Reaction of the opportune metal precursor (Ca[N(SiMe3)2]2(THF)2 or MgnBu2) with one equivalent of the pro-ligand PPP-H produces the corresponding calcium amido (1) or magnesium butyl (2) complex in high yield. Solution NMR studies show monomeric structures and kinetically stable for both species. The obtained complexes efficiently mediate the ring-opening polymerization of ɛcaprolactone showing a TOF up to 40000 h-1. In the presence of a hexogen alcohol, up to 2000 equivalents of monomer are converted by using a low loading of catalyst (5 μmol). Kinetic studies show a first order reaction in monomer concentration

Monoamidinate titanium complexes: highly active catalysts for the polymerization and copolymerization of L-​lactide and ε-​caprolactone

A series of titanium trichloroamidinate complexes with distinct ligand sets showed different abilities in the copolymerization of ε-caprolactone and l-lactide, producing copolymers ranging from gradient to truly random microstructures.</p

Polymerization of ethylene with nickel alpha-diimine catalysts

Several nickel alpha-diimine compounds of the general formula (ArN=C(R)-C(R)=NAr)NiX2 (Ar = 2,6-alkyl substituted Ph, R = H or CH3, X = Br or CH3) were tested in ethylene polymerization after activation with different co-catalysts, such as methylaluminoxane, Al(C2H5)(2)Cl or other aluminium alkyls, and ionizing reagents like B(C6F5)(3), [CPh3][B(C6F5)(4)] or HBF4. The performances of the different catalytic systems were compared with reference to polymer productivity and structure. The degree of branching of the obtained polyethylenes was shown to depend not only on the ligand environment at the Ni centre but also on the type of co-catalyst

Isotactic-specific polymerization of propene with an iron-based catalyst: polymer end groups and regiochemistry of propagation

Prevailingly isotactic poly(propylene) samples were prepared with a homogeneous catalytic system based on a bis(imino)pyridyl Fe(II) derivative and methylaluminoxane. The polymer microstructure is in agreement with Bernoullian statistics of dyad formation, implicating a "chain-end mechanism of steric control. The latter is operative even at polymerization temperatures as high as +50"C. NMR analysis of polymer end groups indicates that chain growth proceeds via 2,l monomer insertion. The last two findings are unprecedented for isotactic-specific polymerization of propene and are reasonably related to each other