The reactions of iodoanilines IC6H4NRR '-2 with [Pd(PPh3)4] gave complexes [Pd(C6H4NRR '-2}I(PPh3)2] [R=H, R'=H (1 a), Me (1 b); R=R'=Me (1 c)] while a mixture of 1 a, and the dimeric [Pd{mu-C,N-C6H4NH2-2)I(PPh3)]2 (2 a) was obtained when the appropriate iodoaniline was reacted with [Pd(dba)2] (dba=dibenzylideneacetone) and 1 equiv. of PPh3. The phosphonium salts [Ph3PC6H4NRMe-2]OTf [R=H (3 b), Me (3 c)] formed upon reacting complexes 1 b,c with TlOTf (OTf=CF3SO3). Complexes of the type [Pd(C6H4NRR '-2}I(N N)] (4) were obtained from the reaction of [Pd(dba)2] with the appropriate iodoaniline and a N N bidentate ligand (N N=4,4 '-di-tert-butyl-2,2 '-bipyridine or N,N,N ',N '-tetramethylethylenediamine). Complexes 4 reacted with TlOTf and PPh3 or XyNC (Xy=C4H4Me2-2,6) to give [Pd(C6H4NRR '-2)(N N)(PPh3)]OTf (5) or [Pd{C,N-C(=NHXy)C6H4NRR '-2)(N N)]OTf (6), respectively. In the absence of any added ligand, the reactions of complexes 4 with TlOTf produced the dimeric complexes [Pd{mu-C,N-C6H4NHR-2)(N N)]2(OTf)2 (7) or the four-membered palladacycles [Pd(kappa 2-C6H4NMe2-2)(N N)]OTf (8), depending on the substitution degree of the aniline reagent.

The synthesis of the previously reported complexes [Pd{(C,C-CHCO2R)(2)PPh2}(mu-Cl)](2) (R = Me (1), Et (2)) has been considerably improved by reacting the phosphonium salts [Ph2P(CH2CO2R)(2)]Cl with Pd(OAc)(2). Complexes 1 and 2 react with isocyanides R'NC (R' = C6H4Me2-2,6 (Xy), C6H4I-2 and Bu-t) to give complexes of the type [Pd{C,C-{C(CO2R) = C(NHR')}(CHCO2R)}PPh2}Cl(CNR')], resulting from the insertion of the unsaturated molecule in one of their Pd-C bonds and the hydrogen transfer from the methine CH to the iminobenzoyl nitrogen. These are the first insertion reactions observed in the Pd-C bond of a P-ylide complex. The crystal structure of the complex [Pd{C,C-{C(CO2Me)=C(NHXy)}(CHCO2Me)}PPh2}Cl(CNXy)] (3) is reported. (c) 2019 Elsevier B.V. All rights reserved.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The complex [Pd{C6H4NHCHO-2}I((t)Bubpy)] (A, (t)Bubpy = 4,4'-di-tert-butyl-2,2'-bipyridine) reacts with CO or XyNC, affording the benzoyl or iminobenzoyl complexes [Pd{C(O)C6H4NHCHO-2}I((t)Bubpy)] (1) or [Pd{C(=NXy)C6H4NHCHO-2}I((t)Bubpy)] (2), respectively. Dehydroiodination of 2 with Tl(acac) (acacH = acetylacetone) produced the iminobenzoyl(amide) complex [Pd{C,N-C(=NXy)C6H4NCHO-2}((t)Bubpy)] (3) from which complex [Pd{C,N-C(=NXy)C6H4NCHO-2}(CNXy)(2)] (4) was obtained upon substitution of the tBubpy ligand with 2 equiv of XyNC. Heating complex 3 in mesitylene at 160 degrees C for 3 h caused (t)Bubpy loss, and the generated coordination vacancies were occupied by the amido oxygen and the iminobenzoyl nitrogen atoms, both acting as bridging ligands to give the tetranuclear species [Pd-4{N,O-{C,N-C(=NXy)C6H4NCHO-2}(4)] (5). Removal of the iodo ligand in A by reacting it with TlOTf (OTf = trifluoromethanesulfonate, triflate) caused coordination of the amido oxygen atom to give the cationic complex [Pd{C,O-C6H4NHCHO-2}((t)Bubpy)]OTf (6) in which the Pd-O bond was split by reaction with XyNC to give [Pd{C(=NXy)C6H4NHCHO-2}(CNXy)((t)Bubpy)]OTf (7). The crystal structures of 3, 5, and 6 have been determined by X-ray diffraction methods.

Oxidative addition of N-(2-iodophenyl)formamide to Pd(dba)2 (dba = dibenzylideneacetone) in the presence of 4,4'-ditertbutyl-2,2'-bipyridine ((t)Bubpy) produces [Pd(C6H4NHCHO-2)I((t)Bubpy)] (1) which inserts 2-iodophenyl isocyanide to give [Pd{C(=NC6H4I-2)C6H4NHCHO-2}I((t)Bubpy)] (2). Dehydroiodination of 2 with Tl(acac) (acacH = acetylacetone) gives the stable Pd(IV) complex OC-6-35-[Pd{C,N,N-C(=NC6H4-2)C6H4NCHO-2}I((t)Bubpy)] (4) likely resulting from the spontaneous oxidative addition of the I-Ar moiety present in the unstable intermediate Pd(II) complex [Pd{C,N-C(=NC6H4I-2)C6H4NCHO-2}((t)Bubpy)] (3). The crystal structure of 4 shows various C-H···O hydrogen bonds resulting in chains of dimers stacked along the a axis.

Orthopalladation of the phenyl ring in the cyclopalladated complex [Pd{C,N-pyl-SCHC(O)Ph}(μ-X)]2 (pyl = 2-pyridyl, X = Cl; 1·Cl) occurs upon reacting it with AgOAc (1 : 2) in MeCN to give the pincer complex [Pd{C,C,N-pyl-SCHC(O)C6H4-2}(NCMe)] (2). The nature of the base and X plays a key role because palladation neither occurs with other bases nor when AgOAc is the base and X is Br, in which case 1·OAc is obtained. In addition, complex 2 is not obtained upon refluxing 1·OAc in MeCN. Complex 2 affords complexes [Pd{C,C,N,S-pyl-SCHC(O)C6H4-2}]n, [Pd{C,C,N-pyl-SCHC(O)C6H4-2}L] (L = PPh3, (t)BuNC, XyNC) or Me4N[Pd{C,C,N-pyl-SCHC(O)C6H4-2}Cl] upon acetonitrile loss, or its replacement by neutral or anionic ligands, respectively. Some such complexes act as metallaligands towards AgClO4 or [PdCl2(NCPh)2] giving rise to heterodinuclear [{Pd{C,C,N-pyl-SCHC(O)C6H4-2}(PPh3)}{Ag(PPh3)}]ClO4 or homodinuclear [{Pd{C,C,N-pyl-SCHC(O)C6H4-2}(Cl)}{Pd(μ-Cl)}]2, [{Pd{C,C,N-pyl-SCHC(O)C6H4-2}(Cl)}{Pd(Cl)(PPh3}] complexes. Some derivatives of complexes 1 were also obtained.

Cyclopalladated benzamidoxime complexes [Pd{C,N-C6H4{C(NH2)[double bond, length as m-dash]NOH}-2}Cl(L)] (L = PTol3, Tol = C6H4Me-4 (); XyNC, Xy = C6H3Me2-2,6 (); pic, C5H4Me-4 ()), [Pd{C,N-C6H4{C(NH2)[double bond, length as m-dash]NOH}-2}(L2)]ClO4 (L = pic (); L2 = 4,4'-di-tert-butyl-2,2'-bipyridine, tbbpy ()) and PPN[Pd{C,N-C6H4{C(NH2)[double bond, length as m-dash]NOH}-2}Cl2] () are prepared by reacting [Pd{C,N-C6H4{C(NH2)[double bond, length as m-dash]NOH}-2}(μ-Cl)]2 () with the appropriate neutral ligand or with [PPN]Cl, respectively. The cationic complexes are obtained in the presence of NaClO4. The reaction of with K(t)BuO affords the dinuclear oximato complex [Pd{μ-C,N,O-C6H4{C(NH2)[double bond, length as m-dash]NO}-2}(PTol3)]2 () or, in the presence of ClCH2py·HCl, the pincer derivative [Pd{C,N,N'-C6H4{C(NH2)[double bond, length as m-dash]NOCH2(C5H4N-2)}-2}(PTol3)]ClO4 (). Complex reacts with XyNC to give the iminobenzoyl complex [Pd{C,N-C(N[double bond, length as m-dash]Xy)C6H4{C(NH2)[double bond, length as m-dash]NOH}-2}Cl(CNXy)] () resulting from the insertion of XyNC into the Pd-C bond. The dinuclear complex [{Pd(tbbpy)}2{C,N,N',O-C6H4{C(NH)[double bond, length as m-dash]NO}-2}]ClO4 () bearing a bridging tetradentate benzimido(oximate) ligand is obtained by reacting Pd(OAc)2 with tbbpy and the metal-ligand complex . The crystal structures of complexes , , and have been determined.

Neutral and cationic six-membered C,N-palladacycles with the core "Pd{C,N-C6H4{CH2C(Me)=NOH}-2}" have been obtained by oxidative addition of the oxime BrC6H4{CH2C(Me)=NOH}-2 to "Pd(dba)(2)" (dba = dibenzylideneacetone) in the presence of mono- or bidentate ligands. The oximato complex [Pd{mu-C,N,O-C6H4{CH2C-(Me)=NO}-2}(PTol(3))](2) forms after dehydrobromination of the appropriate oxime complex with (KBuO)-Bu-t, while the pincer derivative [Pd{C,N,N'-C6H4{CH2C(Me)=NOCH(2)py}-2}Br] results by attack of an in situ generated oximato complex to BrCH(2)py center dot HBr. Insertion of CO or RNC in some of the palladacycles causes a depalladation/coupling process, giving 1,2-dihydro-1-oxo-2-hydroxy-3-methylisoquinoline or 1,2-dihydro-1-imino(R)-2-hydroxy-3-methylisoquinoline, respectively, while the insertion of alkynes produces eight-membered alkenyl(oxime) palladacycles "Pd{C,N-C(R')=C(R)C6H4{CH2C(Me)=NOH}-2}". When using diphenylacetylene, a dimeric tetranuclear complex [{Pd(tbbpy)}(2){mu-N,O-{eta(3)-C6H4(C4Ph4){CH2C(Me)=NO}}}](2)(4+) forms instead, in which a pi-allyl-coordinated oximato, bearing a spirocyclic substituent, acts as the bridging ligand. The crystal structures of the oxime and of each type of complexes have been determined.

Pincer complexes of the types [Pd{C,N,N′-Ar{C(Me)═NOCH2py-2}-2}X] or [Pd{C,N,S-C6H4{C(Me)═NOCH2SMe}-2}Cl] (Ar = C6H4, C6H(OMe)3-4,5,6; py-2 = 2-pyridyl; X = Cl, Br) have been prepared by reacting cyclopalladated oxime complexes [Pd{C,N-Ar{C(Me)═NOH}-2}(μ-Cl)]2 with XCH2py-2 or ClCH2SMe, respectively, in the presence of KtBuO. Various neutral and cationic derivatives have been synthesized as well as iminobenzoyl complexes resulting from the insertion of isocyanide into their Pd–Caryl bond. The cycloaddition of MeO2CC≡CCO2Me to the oximato complex [Pd{C,N-C6H4{C(Me)═NO}-2}(tBubpy)] (tBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine) in the presence of various neutral L ligands produces pincer complexes [Pd{C,N,C′-C6H4{C(Me)═NOC(CO2Me)═C(CO2Me)}-2}L]. Complexes of each one of the new types have been characterized by X-ray diffraction methods.

The complex [Pd{C,N,O-C(=NXy)C6H4{NC(Me)CHC(Me)O}-2}PPh3] (A) reacts with aqueous HCl and H2O2 or with aqueous HCl (HCl:Pd = 2, 3) to produce the complexes [PdCl2{C,N-C(=NHXy)C6H4NH2-2}] (1), cis-[PdCl2{C(= NHXy)C6H4NH2-2}}(PPh3)] (2c), and [PdCl2{C(=NHXy)C6H4NH3-2}PPh3]Cl (3), respectively. The reactions of complex 1 with L (neutral C- or P-donor ligands) give [PdCl2{C(=NHXy)C6H4NH2}-2}L] (2). Dehydrochlorination of 2a (L = (CNBu)-Bu-t) occurred upon heating to give [PdCl{C,N-C(=NXy)C6H4NH2-2}L] (4). The complexes [PdCl{C,N-C(=NXy)C6H4NH2-2}PPh3]X (X = ClO4 (5), TfO (5')) were obtained by reacting 2c with AgClO4 or TlTfO (TfO = CF3SO3), respectively. When 1 was reacted with NEt3, a dehydrochlorination/dimerization process occurred, giving [Pd2Cl2{mu-N,C,N'-C(=NXy)C6H4NH2-2}(2)] (6a), which, in turn, reacted in two steps with TITfO and NaOAc to give [Pd-2(OAc)(2){mu-N,C,N'-C(=NXy)C6H4NH2-2}(2)] (6b). The reaction of 1 with 1 equiv of a neutral ligand L and a carbonyl compound (acetone, RCHO, or R'(CHO)(3)) affords the neutral 1,2-dihydroquinazolinium-4-yl complexes cis[PdCl2{C(=NXy)CMe2NHC6H4-2}L] (7), cis-[PdCl2{C(=NXy)CH(R)NHC6H4-2}PPh3) (8), and [{cis-PdCl2{C(=NXy)CHNHC6H4-2}CNXy}(3){mu(3)-C6H3(C6H4-4)(3)-1,3,5}] (9)), respectively. Depalladation of compounds 7 occurred when they were heated with TITfO, to give 2-Me-4-xylyliminium-1,4-dihydroquinoline triflate (10a). The complexes trans-[PdI{C(=NXy)CMe2NHC6H4-2}(CNXy)(2)]TfO and trans-[PdI{C(=NXy)C6H4NH2-2}(CNXy)(2)] react in two steps with AgTfO and PhC CH/NEt3 to give the depalladated species 2,2-dimethyl-3-xylyl-4-phenylethynyl-1,2-dihydroquinazolinium triflate (11) and H2NC6H4{C(=NXy)C CPh}-2 (12), respectively. Complex 11 reacts with (KBuO)-Bu-t or Tl(acac) to give the dinuclear complex [Pd-2{mu-C,N-C(=NXy)C6H4NH-2}{C,N-C(=NXy)C6H4NH2-2}(CNXy)(3)] (13).

The reaction of [PdI{C,N-C(=NHXy)C6H4NH2-2}CNXy]TfO with XyNC (1:2, TfO = CF3SO3, Xy = C6H3Me2-2,6) gives the cationic carbene complex [PdI{C,C-C(=NHXy)C6H4{NHC(NHXy)}-2}CNXy]TfO (4), while that of [PdCl2{C(=NHXy)C6H4NH2-2}] with isocyanides (1:1, 50-60 degrees C) gives the neutral carbene complexes [PdCl2{C,C-C(=NHXy)C6H4{NHC(NHR)}-2}] (R = Bu-t (8), Xy (9)), from which mono- and dicationic derivatives [PdCl{C,C-C(=NHXy)C6H4{NHC(NHXy)}-2}L]X (L = XyNC, X = TfO (10); L = PPh3, X = Cl (11)) and [Pd{C,C-C(=NHXy)C6H4{NHC(NHXy)}-2}(CNXy)(2)](TfO)(2) (12), respectively, have been isolated. Dehydrochlorination of complex 9 with TlTfO and NaOAc (1:2:2) or with NEt3 (1:1) affords the dinuclear complexes [(Pdx)(2){mu-N,C,C-C(=NXy)C6H4{NHC(NHXy)}-2}(2)] (X = OAc (13), Cl (14)), which in turn react with PPh3 to give [PdX{C,C-C(=NXy)C6H4(NHC(NHXy)}-2}PPh3] (X = OAc (15), Cl (16)). Oxidative addition of 2-iodobenzoic acid to 13 leads to the Pd(IV) complex [{PdI(C6H4CO2-2)}(2){mu-N,C,C-C(=NXy)C6H4{NHC(NHXy)}-2}(2)] (17), while the reaction of 14 with PhICl2 affords the Pd(III) derivative [(PdCl2)(2){mu-N,C,C-C(=NXy)C6H4{NHC(NHXy)}-2}(2)] (18). The crystal structures of 4, 9, and 12 have been determined, and the atomic connectivity in 18 has been established.

The authors wish to add the following statement regarding the synthesis of 3c2 and 3d4: ‘The formation of 3c2 and 3d4 requires to consider the other stereoisomers of intermediates J and H (Scheme 3)’. We thank Professor Joseph M. Muchowski for bringing this omission to our attention. Additionally, some of the data in the fourth column of Table 1 are displaced from their right positions. The correct Table 1 is shown below.

Following the reaction sequence i) oxidative addition of RNHC(O)C6H3I2-2,6 (R = Me, Tol) to [Pd-2(dba)(3)]center dot dba in the presence of chelating ligands N boolean AND N or XyNC (Xy = C6H3Me2-2,6), ii) treatment of the resulting complexes with TlTfO or Tl(acac) (acac = acetylacetonato), and iii) insertion of unsaturated molecules (CO, XyNC, MeO2CC CCO2Me, MeC(O)CH=CH2) into one of the Pd-C-aryl bonds of the resulting complexes allowed the synthesis of aryldipalladated complexes containing the ligands L1 = mu-C,C-{(C)6H(3)C(O)NHR}-2,6, L2 = mu-C,C-{C6H3C(O)NHMe}(C=NXy)(2)-2,6, L3 = mu-C,O,C-{C6H3C(O)NHMe}-2,6, L4 = mu-C,O,C,N-{C6H3C(O)NR}-2,6, L6 = mu-C,N,C,O-{C6H3C(O)NR}-2-(C=O)-6, L7 = mu-C,N,C,O-{C6H3C(O)NR}-2-{C(CO2Me)=C(CO2Me)}-6, L8 = mu-C,N,C,O-{C6H3C(O)NR}-2-(C=NXy)-6 and two arylmonopalladated complexes with the ligands L5 = C,O-{C6H4C(O)NHMe}-2 and L9 = C,N-{C6H3C(O)NTol}-2-{CH=CHC(O)Me}-6. The complex with the ligand L7 inserted CO into the second Pd-C-aryl bond to give an L10-Pd-2 complex (L10 = mu-C,N,C,O-{C6H3C(O)NTol}(C=O)-2-{C(CO2Me)=C(CO2Me)}-6. The dipalladated species display a different environment for each palladium atom and represent the first systems containing two 5 + 5, 5 + 6, 5 + 7, or 6 + 7-membered palladacycles condensed over the central benzamide group. The two arms of the ligands L4 and L6-L8 and LW are "akimbo", and we coin this name both for the ligands and for the dimetallic complexes bearing them. The crystal structure of a [{Pd(N boolean AND N)}(2)L6](+) complex has been determined.

The complex cis-[PdCl2(CNC6H3Me2-2,6)(PPh3)] has been prepared and fully characterized. Its crystal structure has been determined showing the chloro ligands in cis-disposition. A VT-NMR study shows this complex to be in equilibrium with trans-[PdCl2(PPh3)2] and cis-[PdCl2(CNC6H3Me2-2,6)2]. The equilibrium is fast at room temperature but at −50°C all three species are observed in solution in 10:1:1M ratio. The activation parameters for this equilibrium have been calculated.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

A straightforward synthesis of substituted 1,2-dihydroquinazolinium triflates (3) is reported by reaction of 2-imino-substituted anilines with a range of carbonyl compounds in the presence of triflic acid via intermediate iminium salts. Similar reactions with di- or trialdehydes and triflic acid give bis- or tris-(1,2-dihydroquinazolinium) salts. Some 4-methyl substituted 1,2-dihydroquinazolinium salts rearrange, under various conditions, to their corresponding 4-iminium-1,2,3,4-tetrahydroquinolinium isomers (7). Most of salts 3 derived from ketones are rather unstable, which prevents their isolation or full characterization. The crystal structures of various 3 and 7 salts have been determined.

Complexes [Pd{C,N-Ar{C(Me)=NOH}-2}(μ-Cl)](2) (1) with Ar = C(6)H(4), C(6)H(3)NO(2)-5 or C(6)H(OMe)(3)-4,5,6, were obtained from the appropriate oxime, Li(2)[PdCl(4)] and NaOAc. They reacted with neutral monodentate C-, P- or N-donor ligands (L), with [PPN]Cl ([PPN] = Ph(3)P=N=PPh(3)), with Tl(acac) (acacH = acetylacetone), or with neutral bidentate ligands N^N (tetramethylethylenediamine (tmeda), 4,4'-di-tert-butyl-2,2'-bipyridine ((t)Bubpy)) in the presence of AgOTf or AgClO(4) to afford complexes of the types [Pd{C,N-Ar{C(Me)=NOH}-2}Cl(L)] (2), [PPN][Pd{C,N-Ar{C(Me)=NOH}-2}Cl(2)] (3), [Pd{C,N-Ar{C(Me)=NOH}-2}(acac)] (4) or [Pd{C,N-Ar{C(Me)=NOH}-2}(N^N)]X (X = OTf, ClO(4)) (5), respectively. Complexes 1 reacted with bidentate N^N ligands in the presence of a base to afford mononuclear zwitterionic oximato complexes [Pd{C,N-Ar{C(Me)=NO}-2}(N^N)] (6). Dehydrochlorination of complexes 2 by a base yielded dimeric oximato complexes of the type [Pd{μ-C,N,O-Ar{C(Me)[double bond, length as m-dash]NO}-2}L](2) (7). The insertion of XyNC into the Pd-C(aryl) bond of complex 2 produced the mononuclear iminoaryloxime derivative [Pd{C,N-C(=NXy)Ar{C(Me)=NOH}-2}Cl(CNXy)] (8) which, in turn, reacted with [AuCl(SMe(2))] to give [Pd{μ-N,C,N-C(=NXy)Ar{C(Me)=NOH}-2}Cl](2) (9) with loss of XyNC. Some of these complexes are, for any metal, the first containing cyclometalated aryloximato (6, 7) or iminoaryloxime (8, 9) ligands. Various crystal structures of complexes of the types 2, 3, 6, 7, 8 and 9 have been determined.

Spontaneously or under various heating conditions, 2-alkyl- or 2-aryl-(iminoalkyl)benzenamines react with ketones and triflic acid (1:1:1) to give quinolinium salts. When working under milder thermal conditions, intermediate 1,2-dihydroquinazolinium derivatives can be isolated or detected in solution but decompose upon standing or heating to give the corresponding quinolinium salts.

The crystal structures of trans-[PdI{C=N(Xy)CH(R)NHC6H4-2}(CNXy)(2)]OTf (R = Me (1 center dot CHCl3) space group P-1, a = 8.7665(4) , b = 15.5346(8) , c = 16.2415(8) , alpha = 72.698(2)A(0), beta A = 78.310(3)A(0), gamma A = 88.310(2)A(0), CH = CH2 (2 center dot 0.5Et(2)O) space group P2(1)/c, a = 15.7868(6) , b = 14.5066(6) , c = 18.5814(7) , beta = 106.707(2)A(0), C6H4Me-4 (Tol) (3) space group P-1, a = 11.96075(5) , b = 12.9452(51) , c = 13.1263(5) , alpha = 93.306A(0), beta A = 95.822(2)A(0), gamma A = 94.572(2)A(0)) have been measured. The structural data suggest the existence of some electron delocalization over the heterocyclic ring, the extension of which seems to depend on the R substituent. The complex [PdI{C6H4(N=CHTol)-2}(bpy)] (Tol = C6H4Me-4, bpy = 2,2'-bipyridine, 4) is the fourth imino-substituted aryl palladium complex. Complex 4 crystallizes in triclinic P-1 with a = 8.7873(5) , b = 8.8936(5) , c = 13.8375(8) , alpha = 90.116(2)A(0), beta A = 92.760(2)A(0), gamma A = 106.243(2)A(0).